The Big Bang Theory



"Leonard: Okay, well, I'm an experimental physicist at Caltech. Most of my research involves high powered lasers. Oh, and I just got a government grant to see if they can be used to knock out incoming ballistic missiles. Penny: Wow! Can they? Leonard: Oh God no! (long pause) But the money's good... and I used the equipment to build my own Bat Signal."

The Big Bang Theory is a CBS Sitcom, which debuted on September 24, 2007 and ended on May 16, 2019, with four genius level friends (ranging from theoretical physics to engineering) and a pretty girl who shakes up their normally scientific method-filled life.

The main characters are two Odd Couple roommates, Leonard Hofstadter and Sheldon Cooper. Leonard is a mild-mannered Nerd who, although awkward, is still socially capable. Sheldon is an egomaniacal supergenius who displays signs of OCD, ADHD and Asperger's Syndrome.

A cute new neighbour called Penny moves in next door, and Leonard almost instantly develops a crush on her. Penny is a perfectly normal person with an average intelligence level, but is seen as a Dumb Blonde compared to Leonard and Sheldon.

Rounding out the cast are two other genius geeks who are always visiting Sheldon and Leonard: Howard Wolowitz, a a wild but unsuccessful womanizer who never stops hitting on Penny; and Rajesh "Raj" Koothrappali, who suffers from crippling shyness whenever attractive women are around (unless he's drunk or otherwise intoxicated).

The show's humor can be divided into three categories: obscure references to physics or Geek culture (including discussions of the Three Laws of Robotics and the metaphysics of teleportation), every Nerd stereotype the writers can think of (including Halo, Star Trek, Star Wars and Basement Dwellers) and the culture clash between Penny and the guys (after Sheldon tries to explain what semiotics is, Penny replies "Okay, sweetie, I know you think you are explaining but you're not!").

And for the most part the scientific and nerd references are accurate, or at least close enough that somewhere between the writing and the acting someone knows what they're talking about. As for the show's drama and overarching plot, most of that relies on UST between Leonard and Penny. The series almost runs on Give Geeks a Chance.

Starting in season four they added two new characters as semi-regulars, Bernadette Rostenkowski (Microbiologist) and Amy Farrah Fowler (Neurobiologist). Bernadette was Penny's friend and co-worker who began dating Howard. Amy is a female counterpart and asexual love interest to Sheldon accidentally discovered through an online dating service prank. While they are also extremely intelligent, they ended up forming a trio with Penny that contrasts the four guys and gives a new female perspective on the show.

View character sheet.

0-E
"Leonard: Does the fact that you've been drinking and that you're angry at Kurt have anything to do with this? Penny: It... might. (sigh) Wow, you are really smart! Leonard: Yeah, I'm a FREAKING genius. Penny: You are so great, why aren't all men like you? Leonard: Because if all men were like me, the human race wouldn't survive!"
 * 419 Scam: A "Nigerian prince" offers to track Sheldon's stolen World of Warcraft equipment for a fee.
 * Above the Influence: Leonard in "The Middle Earth Paradigm". After a brief confrontation between Leonard and Penny's ex at her Halloween party, Penny visits Leonard in his apartment a little drunk and upset over what happened. Leonard ends up comforting her and she starts kissing him. While obviously enjoying it, he pulls away:

"Sheldon: You know Germans have an interesting pre-wedding custom- Howard: Then it probably isn't for me!"
 * Abusive Parents: Leonard's mother is emotionally abusive and neglectful. Naturally this is Played for Laughs.
 * Accidental Hero: Sheldon on multiple occasions. He really liked Leonard's girlfriend mid-season two, Dr. Stephanie, and thus worked extra hard to try and make their relationship work. It got to the point he hacked Leonard's Facebook profile and sent a relationship request; when Leonard found out he was furious, although it turned out okay when Stephanie confirmed the request. When Leonard and Penny broke up late season three, it was his antics trying to be with both Penny and Leonard that ended up getting the two back to being friends.
 * Accidental Kiss: When a drunk Rajesh attempts to kiss Bernadette, Howard gives a Big No and interposes himself between the two. And he doesn't kiss his girlfriend.
 * Acceptable Feminine Goals: Despite being a renowned scientist with a brilliant career, Amy believes strongly in those, mostly because she was always deprived of ever believing it could be a possibility for her in the first place.
 * Acquired Situational Narcissism: Rajesh, episode "The Griffin Equivalency." At the least, he is drunk throughout most of the episode and when drunk he tends to be somewhat insufferable regardless of the situation.
 * Actor Allusion: In one episode, Kaley Cuoco's character Penny is talking about an upcoming play and says, "This could be my only chance to play Anne Frank." In 8 Simple Rules, Kaley Cuoco's character Bridget was Anne Frank in her school play.
 * Penny later got a commercial gig that showed her riding horses. Kaley is an avid rider, and in fact broke her leg the previous season after she fell and the horse trotted over it.
 * Courtney Ford showed up as a geeky girl and made a reference to Superman. Ford is not only quite geeky herself but is married to Brandon Routh of Superman Returns.
 * In an early episode, the boys consider recruiting "TV's Blossom" (Mayim Bialik) to their Physics Bowl team, as Raj has heard she has a Ph.D. in "neuroscience or something." Dr. Bialik does, in fact, have a Ph.D. in neuroscience, and later appeared on the show as Amy Ferrah Fowler, a neurobiologist.
 * Adam Westing: Wil Wheaton.
 * Adorkable: Duh.
 * Afraid of Needles: Leonard is so afraid of having to get stitches for his hand that he vomits - and when Howard sees them, so does he.
 * All Germans Are Nazis: Subtly invoked to nip Sheldon's bachelor party suggestion in the bud;
 * All Germans Are Nazis: Subtly invoked to nip Sheldon's bachelor party suggestion in the bud;

"Janitor: Here, I am janitor. In former Soviet Union, I am physicist, Lenigrad Polyteknika. *Beat* Go Polar Bears!"
 * All Girls Want Bad Boys: Penny seems to be attracted to muscular and obnoxious guys (Kurt from the pilot episode and the unseen boyfriend of the first season finale) and subsequently hates herself for it. One of the main reasons she gives Leonard a chance is that he was so far removed from the previous guys she would date.
 * Inverted in "The Flaming Spittoon Acquisition" with Sheldon, Amy and Stuart.
 * All Just a Dream: The majority of.
 * All Psychology Is Freudian:
 * Leslie (not to mention Howard and Sheldon) is convinced Penny's addiction to Age of Conan is a result of sexual frustration.
 * Averted and played straight by Leonard's mother, a psychologist (and TV Genius ala Sheldon), who acknowledges briefly that many of Freud's theories are obsolete. She still uses informal Freudian analysis on Penny, Howard, and Raj, the latter of whom she insists are in an ersatz homosexual relationship. They immediately begin arguing the point... Like an Old Married Couple.
 * All Women Love Shoes: Penny, many examples.
 * Almighty Janitor: The janitor in "The Bat Jar Conjecture".

"Raj (to Howard): Last night I had a dream, we got so rich from the app we made, you and I bought matching side by side mansions. But, there was a secret tunnel connecting your front yard to my back yard. What do you think it means? Howard: It means next time we play handball I'm showering at home."
 * Ambiguous Disorder: Sheldon. Leonard's mother Beverly. Amy. They all have something going on, being exaggerated versions of every geek and aloof-genius stereotype you've ever heard of. This leads to a good amount of fan speculation that one or all have Asperger's Syndrome in some form. Jim Parsons has also stated that Sheldon "could not have more symptoms of Asperger's" but also stated the writers have not done it intentionally and he hasn't played Sheldon that way.
 * Ambiguously Gay: Raj. His sister even admitted that his family was wondering that about him. But besides some awkward moments both in the show and spoken of in passing, it's made pretty clear that he isn't gay... through a series of daydreams about his attraction to Bernadette. "Dance number aside, I am SO not gay." so he may be more Camp Straight.
 * There was that time Leonard's psychiatrist mother described Raj and Howard as being in "an ersatz homosexual relationship".
 * In the episode before he daydreams about Bernadette, however...

"Sheldon (to Amy regarding letting Penny cut his hair): Amy, what do you think? Amy: There's not a hair on my body I wouldn't let this woman trim."
 * Amy has all but stated she has a big crush on Penny (and has admited Bernadette as well), but could be interpreted as a Stupid Sexy Flanders in that she appreciates her own gender but is otherwise straight.

"Leonard: I can't believe you're going to have Howard choose between sex and Halo! Sheldon: No, I'm asking him to chose between sex and Halo 3. As far as I know sex hadn't been upgraded to include hi-def graphics and advanced weapon systems. Leonard: Right, all sex has is nudity, orgasms and human contact. Sheldon: My point."
 * Amicably Divorced:
 * Amusing Alien: Sheldon Cooper is an Earthling example.
 * Anachronism Stew: In-universe at a Renaissance Faire the main characters attend, with historical inaccuracies discussed by Sheldon. Later, Sheldon invents Three Person Chess and adds several new pieces and rules to the game, the result being that the medieval-styled classical chess pieces can now move using golf carts, time machines, transporter pads and jetpacks.
 * Armor-Piercing Question: In a girl's night out when they ended up playing "Truth or Dare" Bernadette asked Penny why she hung out and talked with Leonard so much even though she broke up with him. Penny replied that he was a great guy but felt he got too serious, which led to another question that what if she wanted him back and he was taken by someone else because he is a "great guy?" Penny didn't know how to respond to that and declared the game over.
 * Arson, Murder, and Jaywalking: Howard compares the reception to one of Sheldon's lectures to "the Hindenburg meets Chernobyl meets Tron 2".
 * The Art of Bra Removal: Howard is making out with Bernadette and fumbling with her bra, only for her to tell him it unhooks at the front.
 * Ascended Extra/Demoted to Extra: Leslie Winkle showed up three times in the first season, and her character was liked enough that the production team announced her as becoming a regular early in the second season. After about 4 episodes in they quickly realized that she worked largely because she was a staunch, stubborn Arch Enemy to Sheldon with no real room for her own stories or even Character Development. They quietly put her character aside and she shows up more sporadically since.
 * Both Bernadette and Amy Farrah Fowler started out as sporadic recurring characters introduced in the third season and given their own little plot lines in the fourth. While they may not always show up unlike the core 5, they are credited as stars in the episodes they appear, and have appeared much more frequently than before. Starting from season 5, they can be expected to appear in any given episode and get just as much focus as any of the other characters.
 * Asexuality: This is Sheldon's 'deal'. He's familiar with the concepts of physical or romantic attraction but doesn't apparently experience those things himself. Any time he "clicks" with someone in a romantic way, it is always juxtaposed with a common scientific enthusiasm. While the possibility of sexual attraction has appeared from time to time, he is written largely as someone who puts intellect and science first and mocks his friends for not doing the same.

"Amy: "When she walks, she's like a samba that swings so cool and sways so gentle that when she passes, each one she passes goes..." Sheldon: (Knock, knock, knock) Amy? (Knock, knock, knock) Amy? (Knock, knock, knock) Amy?"
 * Similarly his Not-Girlfriend/Distaff Counterpart Amy Fowler refuses to touch or have sex with him. But the more she hangs out with Penny she displays more signs of sexual repression rather than straight asexuality, along with hints towards seeing the appeal of either side.
 * Further realized when Amy gets roaring drunk and demands to know what or how much it would take for Sheldon to "take her to that skeezy motel and ravish her."
 * Astonishingly Appropriate Interruption: In the second Season 5 episode, Amy Farrah Fowler is playing the harp and singing "The Girl From Ipanema" when Sheldon pays her a visit.

"Sheldon: (Knock, knock, knock) Penny: WHO DO WE LOVE? Sheldon: Penny?"
 * Also invoked by Penny, who knows that Sheldon always knocks on her door in a certain way with three knocks and then saying her name:

"Penny: What's wrong with Goofy? Leonard: Beats me... he's fine with Pluto."
 * Attention Deficit Ooh Shiny: Sheldon. Penny sometimes, most often when she attends any of their science lectures but there is also this gem "My mother smoked pot when she was pregnant with me and I turned out fine... Oh, more wine!"
 * Audio Erotica: Raj wants Howard to tell his new deaf love interest that he has a deep sexy voice like James Earl Jones, not realizing she wouldn't know the appeal anyway.
 * Bad Bad Acting: Sheldon and Amy trying to put on a web series "Fun with Flags." They always stare straight into the camera, even when having a "conversation" with each other.
 * Barrier-Busting Blow: Penny is casually climbing upstairs, minding her own business, when Sheldon and Leonard's door bursts apart and a killer robot of their own invention rampages into the hallway, making her flee in terror.
 * Howard tries to perform one, but just bounces right off the door.
 * Basement Dweller: Howard, only without the basement apartment. He essentially lives like he's still 15 for American standards, though he and his family are Jewish, which is one of the cultures where adults living with one's parents before getting married is considered normal.
 * The Beard: Penny asked Leonard to pretend that they are still together when her father came to visit, because Leonard is "the first guy he ever approved of. You're a scientist, you went to college, you don't have a neck tattoo or outstanding warrants... or a baby." Leonard, delighting in the irony, proceeds to make out with her at every opportunity.
 * Amy asked Sheldon to pretend to be her boyfriend so that her mom would get off her back. Sheldon initially confused it for an invitation to actually be her boyfriend, and was relieved when that wasn't the case. As they meet her mom over web cam, he made certain to talk about how much sex they have together.
 * Raj is set up by his parents with an Indian girl who admits she is a lesbian and wants to marry him to dispell suspicion. A twist is that she (and others, including his friends and parents) think that Raj is in the closet as well so it would be a mutual beard relationship.
 * The Bechdel Test: Narrowly succeeds. Penny being the sole prominent female character, it was to be expected but the later addition of Bernadette and Amy to the cast, gives the girls more opportunities to occasionally speak about something else than men. Relationship issues usually comes up with their various get-togethers, as each have a romantic counterpart on the guys side, but on the whole they aren't always just talking about men (they actually had a "Truth or Dare" game where Penny ended it when they asked some uncomfortable questions about her feelings for Leonard).
 * Bedmate Reveal: In the final episode of season 4, Raj and.
 * Berserk Button: Sheldon has more buttons than the Great Glass Elevator.
 * Don't mention Wil Wheaton around Sheldon, unless you want a "WHEEEEEAAAATOOOOOONNN!" that would make Shatner proud.
 * They made up at the end of "The Russian Rocket Reaction" and are now good friends (according to Sheldon, anyways). Unfortunately, Brent Spiner then inadvertently replaces Wil Wheaton on Sheldon's Mortal Enemy list.
 * Also for Sheldon... Goofy

"Sheldon: I've had unilateral control of the thermostat since the Sweaty Night of '06."
 * This is a reference to a 1 panel webcomic strip known as "It's Goofy Time". Sheldon's dialogue is a direct copy of the non-goofy character from it.
 * And don't sit in Sheldon's spot on the couch. You will regret it.
 * While Sheldon is perfectly fine with cheap shots aimed at his mother, do not insult his memaw.
 * You do not touch the thermostat.


 * Hating trains is also a friendship-ender for Sheldon.
 * On a similar note, do not mention Sheldon within earshot of Leslie Winkle unless you want to get her to join your effort to subject Sheldon to a Humiliation Conga.

"Like the supporting character in a movie where they disappear for much of the second reel, only to return in the third act coming to the rescue, I have a solution... (complete silence) Odd, they usually cheer."
 * Bested At Bowling: Sheldon, by Wil Wheaton.
 * Beta Couple: Both Bernadette/Howard and Amy/Sheldon are relatively stable compared to Penny and Leonard's relationship. As of "The Herb Garden Germination",  - and in the season 5 finale,
 * Between My Legs: This shot is used with Penny's legs framing a remote control car with a camera that's trying to see... well, between her legs.
 * Beware the Nice Ones: Bernadette, several times in Season 5. In "The Skank Reflex Analysis," when she snaps on Raj, after Leonard reveals to the group Raj's crush on her. Bernadette flips out and angrily confronts Raj, berating him to tell Howard that nothing is going on between the two of them. This is somewhat Lampshaded in the scene.
 * Then again in "The Recombination Hypothesis." Bernadette flat-out states to Howard that she is a "vengeful person" and has access to "weaponized smallpox" if Howard were to ever hurt her.
 * Bernadette, when pushed far enough (which doesn't take much due to her short temper), screams/talks in the same manner as Howards's mother; he finds this sexy. Although Bernadette is more of a Yangire than an actual nice one.
 * Penny assumes her friend Emily is automatically nice because she's deaf, and people with disabilities can't afford not to be kind to everyone. Not quite.
 * Bernadette with children.
 * Believe it or not, Sheldon. He has on numerous occasions talked about using chemicals untraceable in autopsies against his enemies and has the same temper when something gets under his skin that Bernadette does, shouting out angry yet often childish insults in the same way.
 * Big Badass Bird of Prey: Sheldon's perception of the avian creature hanging out on his apartment windowsill, in 'The Ornithophobia Diffusion' (he calls it a "blue jay", thus proving bird identification is not his forte'- it's actually a black-throated magpie-jay.) But after Bernadette finds the bird and demands that he give the creature a pat, he reluctantly goes along with it, and with no negative results, Sheldon does a Heel Face Turn and loves the bird.
 * Big Book of War: The Roommate Agreement
 * Big Brother Instinct: Sheldon briefly becomes very protective of who his twin sister dates, though subverted as its only because he comes to the conclusion that residing in her loins possibly lies the potential building blocks for her to have an offspring who is another remarkable individual like himself; Sheldon 2.0, if you will.
 * Cue one Groin Attack from Missy.
 * Big Damn Heroes: Sheldon describes this trope as well as merging it with Changed My Mind, Kid to explain a resolution when Raj was getting downsized and possibly deported.

"Amy Farrah-Fowler: I used to take my lunch down to the maintenance room and eat with the janitor. It was nice until his wife called me a 'puta' and made me stop."
 * Big No:
 * Sheldon lets one out when he realizes that he locked himself out of his apartment, ruining his perfect night alone.
 * Sheldon when a "terrifying" song bird flies through the apartment window and lands on his couch space.
 * Raj when he gets too attached to the female voice on his phone, has a sex-dream about her as a woman, only to find out that once again, he can no longer speak.
 * Bilingual Bonus: Amy Farrah-Fowler invokes this in Episode 22 of Season 4. You can still get the gist of the sentence, but Amy was called a whore in Spanish.

"Leonard: Are you even listening to me? Sheldon: Of course I'm listening. Blah, blah, hopeless Penny delusion, blah, blah, blah."
 * Chinese speakers will recognize that Sheldon asking the Chinese restaurant owner to "show me your mucus" in "The Tangerine Factor" is indeed a very mangled attempt to say "show me your tangerine peels".
 * Birthday Hater: Sheldon has some mental scars from past birthdays relating to his general aversion to socialization. Leonard is pretty apathetic as far as birthdays go because his mother didn't like the concept, but appreciates the gesture when his friends plan a surprise party for him.
 * Bi the Way: Amy seems to be largely heterosexual, but has made sexual overtures more than once to Penny.
 * Blah Blah Blah:

"Howard: Your dad's a gynecologist! He drives a Bentley!"
 * Bland-Name Product:
 * "I have no difficulty believing you're not butter."
 * Leonard, Penny, and Sheldon watch an episode of Oshikuru Demon Samurai. The actual dialogue heard played is from real series Boogiepop Phantom. Oshikuru is a fictional anime series also mentioned in Two and A Half Men.
 * While the show accurately describes the premises of both Age of Conan and World of Warcraft, any specific location, weapon, or other equipment mentioned in the show is probably fake. For now, at least; Blizzard has no problem embracing a fictional representation of WoW.
 * However, in "The Zarnecki Incursion," many of the WoW references were true to the game.
 * Blind Date: Penny sets Raj up with a Disabled Love Interest.
 * Howard meets Bernadette through a blind date, after Leonard convinces Penny to have one of her friends go on a double date. It goes poorly until they bond over their overbearing mothers.
 * Body Backup Drive: Sheldon wants to do this, but is concerned that the technology won't be ready by the time his body dies.
 * Bollywood Nerd: Raj milks this for all it's worth, claiming to have grown up in poverty before moving to America to pursue his dream of becoming an astrophysicist.

"Sheldon: Am I correct in assuming that your attempt to be accepted by Penny's peers is based on your desire to continue your mating privileges with her? Seems like an awful lot of trouble to go through for intercourse. Don't you have access to women who will do it for money? By the way, another accepted use of the term 'ho'."
 * He later admitted that he grew up in a large home with servants and according to him "We don't allow our poor people to have dreams."
 * Book Dumb: Although Penny is more street-smart, sociable, and tolerant than any of the guys, she's easily exasperated and put off by even trying to learn anything related to science. Except that fig Newtons are named after the town in Massachusetts, not the scientist.
 * "Don't write that down!"
 * This dynamic is reversed in "The Thespian Catalyst", where Penny, during an acting lesson to Sheldon, suggests they read lines from Tennessee Williams' Pulitzer Prize-winning play, Cat on a Hot Tin Roof. Sheldon has no idea who Tennessee Williams is, and insists they work with his own Star Trek fanfiction.
 * Break the Haughty: Sheldon is sometimes caught up by karma. The rest of the gang occasionally succeeds in proving him wrong, humiliating him or shutting him up but it's subverted by the fact that he never seems to lose his arrogance.
 * Breaking Bad News Gently: Leonard says he's in bed when told to sit down.
 * Breaking in Old Habits: Howard + cutting-edge robotic hand.
 * Brick Joke:
 * Another occurs in one episode when Wolowitz, Raj, and Leonard reveal in a passing joke that they always thought that Sheldon reproduced asexually via mitosis. At the very end of the episode, Leonard has a nightmare about this very thing happening, after not being mentioned for half an episode.
 * There's an extremely delayed one hiding in the first episode. The "200-pound transvestite with a skin condition" shows up in the flashback episode at the end of season 3.
 * In "The Creepy Candy Coating Corollary", Leonard says "Warlord beats Troll, Troll beats Elf, Elf beats Water Sprite, and basically everything beats Enchanted Bunny". During Sheldon & Raj's final match with Wil Wheaton and Stuart,
 * Another one in Season 3. In the first scene, Raj, Howard and Leonard run down the stairs shouting "Kites ho!", incurring Sheldon to give a speech on the correct use of the term 'ho'. Later, when Sheldon asks why Leonard went through the trouble of learning the rules of American football so as not to embarrass himself in front of Penny's friends - and therefore still be able to see her - when he could have more easily paid someone else to have sex with him.

"Sheldon: Raj told me to put guys before women who sell their bodies for money. Leonard: Did he say "bros before hoes"? Sheldon: Yes, but I didn't want to offend the hoes."
 * Which becomes a brick joke again in another episode:

"Sheldon: Dr. Stephanie is the only person Leonard has dated that I can tolerate. Penny: Hey! What about me? Sheldon: ...the statement stands for itself."
 * "Your check engine light is on."
 * Brief Accent Imitation:
 * Howard occasionally imitates an exaggerated Indian accent. For example, in “The Grasshopper Experiment” he pretends to be Raj on the phone.
 * Once, when high on hippie cookies, Raj made fun of Leonard's American accent by replicating it with a surprisingly good American accent of his own.
 * In the fourth season finale, Penny does a pretty good impression of Raj's Indian accent.
 * Brilliant but Lazy: Leonard, at least according to his mother and Sheldon. Both express the opinion that Leonard is slumming it by doing no original research and baffled at why he's content confirming the results of experiments done by others.
 * Leonard does point out that confirming results validates the major scientific experiments and that just because its not cutting-edge research, doesn't mean its not very important work. When Sheldon came up with a new theory that was highly praised, Leonard was quick to remind him that he created the experiment that proved it; the scientific community wouldn't just "take his word for it".
 * Brutal Honesty: Sheldon is a practitioner.

"Amy: *drunk* What would it take for you to go into that liquor store, buy a bottle of hooch, then go to the motel over the street and have your way with me?"
 * But I Would Really Enjoy It: Amy invokes changing the physical parameters of her relationship with Sheldon at various points.

"Amy: Proposal: one wild night of torrid lovemaking that soothes my soul and inflames my loins."

"Amy: Are you familiar with meme theory? Sheldon: I'm familiar with everything... but go on."
 * Butt Monkey: Wolowitz. Raj has taken over as the primary Butt Monkey, although really all four nerds take it in turns.
 * But Thou Must!:

"Raj: I'm telling you dude, the only way to make you feel better about Penny going out with other guys, is for you to get back on the whores. Howard: ... "horse". Raj: What? Howard: The phrase is "get back on the horse"... not "whores". Raj: That's disgusting, dude!"
 * But You Screw One Goat!: What Raj believes "get back on the horse" means.

"Raj: Wait, you don't want to put a bite of that in your mouth without trying my homemade chantilly cream! Beat Raj: Yeah ok, that time I heard it!"
 * California University: Averted; Caltech is of course a real (and well-known) university in Pasadena, CA. In a strange variation though, given the ages of each character it is unlikely they would have stayed with the same university as long as they have, at least since about 2002. It's largely just practical for the purposes of a show but it could also be that they are just comfortable with the current status of their careers.
 * Call Back: Early in the second season you catch the tail end of a conversation Penny was having with a boyfriend of the week, where she was trying to explain Schrödinger's Cat to him. In the first season Sheldon used that principle of quantum physics as an analogy towards the possibility of a relationship between her and Leonard. This also doubles as foreshadowing, showing that Penny is starting to enjoy or at least retain the scientific concepts and mental exercises the others often explain to her.
 * In the fourth season Penny gave Leonard a surprise kiss in front of her father, trying to placate him by pretending her and Leonard were together. Leonard stumbled back into his apartment and explained what happened to the guys, and they started joking over Leonard pining after Penny again, with Raj making a direct quote from the pilot episode as a Leonard classic "Our children will be smart and beautiful."
 * In season 1, a sick Sheldon asks Penny, who is nursing him, to sing him a song his mother use to sing to him when has sick, "Soft Kitty." The next season, Sheldon was homesick after being locked out of his apartment and asks Penny to sing the song to him, seeing homesick as a type of sick. The following season, after Sheldon is betrayed by the guys, Penny attempts to console him with "Soft Kitty," but is interrupted by Sheldon since 'Sad is not sick.' Again in the third season, when Sheldon is taking care of Penny after she dislocated her shoulder and was doped up on pain medication, she asks him to sing the song to her.
 * In Season 5, Sheldon's mom actually sings it to him.
 * Calling Your Bathroom Breaks: Sheldon actually insists on a bathroom schedule, occasionally attempting to discuss it with others. Leonard's mother, likewise, stands and says "I have to urinate," before going to the bathroom.
 * Cameo: In the episode where Raj gets in People Magazine's "Top 30 under 30", he brags about it to Charlie from Two and A Half Men, who tells him to call when he's on the cover. (This is a direct reference to the fact that Charlie Sheen has indeed been on the cover of People many, many times.)
 * Camp Straight: Apparently the reason why many people (including his parents) think that Raj is gay, much to his chagrin;

"Sheldon: Fascinating."
 * Can't Hold His Liquor:
 * Sheldon. In a later episode, he uses tequila as an impromptu mouthwash and admitted he might have swallowed a teeny bit. He immediately follows by an offhand "I love you so much" to Leonard. Even coffee to keep him awake makes him quite hyperactive.
 * Likewise, Amy.

"Penny: Sing "Soft Kitty" to me. Sheldon: "Soft Kitty" is for when you're sick. You're not sick. Penny: Injured and drugged is a kind of sick"
 * In an interesting case of Reality Ensues, Raj finds that he can't talk to woman without a little bit of a buzz (it has sometimes just required one sip or at least the Placebo Effect). Initially, while capable of talking to women he also very quickly became drunk and obnoxious. As he continued, his ability to hold his liquor improves drastically, and that trailed into his success with women.
 * Caretaker Reversal: In season 1, Sheldon gets sick and makes Penny take care of him. In season 3 Penny gets injured and makes Sheldon take her to the hospital and take care of her afterward. What connects these two instances most solidly is the song "Soft Kitty." Sheldon teaches the song to Penny to sing to him ('cause that's what his mother did when he was sick as a youngster). Then when Penny is injured she makes him sing it to her.

"Howard: Oh, my God... GIRLFIGHT! [pins Leonard's arms behind his back] Leonard: What're you doing? Howard: I know you, you're stupid enough to break it up!"
 * Casanova Wannabe:
 * Howard.
 * Also, Raj when he's drunk—although at those times he often also has at least a touch of Casanova, Depending on the Writer... or the type of intoxication.
 * The Cast Showoff: Leonard has been shown playing the cello, Howard and Sheldon both play the piano. And they sing!
 * Amy plays the harp and sings as well.
 * Casting Gag: The actors who play Leonard and Leslie previously played David and Darlene on Roseanne. Sheldon's mother is played by Laurie Metcalf, also from Roseanne. Christine Baranski co-starred in Cybill, also written/produced by Chuck Lorre (who was writer/producer for Roseanne).
 * Catch Phrase: Sheldon created his own with "Bazinga!" whenever he attempts a joke or prank. Unusually, it is only used a handful of times a season.
 * This also somewhat crosses over with Germans Love David Hasselhoff in the dubbed Latin American version of the show constantly has Sheldon (through spanish dub voice actor) constantly say the phrase "Vacilon!" almost endlessly even when he appears to mouth something else completely different in English.
 * "Here we go...." whenever someone causes Sheldon to go into an explanation he has apparently said previously numerous times.
 * Cat Fight: Occurs when Penny and new neighbor Alicia's rivalry over her leading Raj, Leonard, and Howard on culminates in a "What're you gonna do about it, bitch?"
 * Somewhat lampshaded by Wolowitz:

"Sheldon's Date: So, Flatland is not only a mathematical essay, but also a treatise on the social mores of Victorian England. Sheldon: You know, I never considered that! That is going to completely change my visits there."
 * Celibate Eccentric Genius: Dr. Sheldon Cooper before Amy Farrah Fowler came along. Even his dynamic with Amy isn't particularly conventionally romantic.
 * In the backstory Leonard's parents only had sex in order to procreate. Once that was done, they were done.
 * Celebrity Paradox: The geeks have a discussion about both Danica McKellar and Mayim Bialik in one first-season episode. It would've been weird enough if just the former had played a bit part later in the series, but when the latter plays Sheldon's date, this gets a bit weirder...
 * Character Development: At the beginning, Penny was a girl who wouldn't ever date someone like Leonard and Leonard wasn't a guy who understood what a relationship with a "normal" girl really meant. They both had to change a lot before they could realistically become a couple.
 * When Howard started dating Bernadette, he grew out of his Casanova Wannabe tendencies and learned to be in a real relationship (it's implied that he never had a third date with the same woman before). This culminates in him being the first member of the group to get married.
 * Howard's sincere and heartfelt apology to Bernadette after she learn how he used to be, admitting that he's no longer that creepy loner since he met her and that she's the reason why he's become a better man. This actually ends up reducing Penny to tears at how far he's come since they first met.
 * Raj has come to master the art of drinking to talk to women but not so much to become an obnoxious slob. In season five, he talked to Penny while completely sober.
 * Sheldon, despite all of his eccentricities and very regimented lifestyle, has come to appreciate social interaction much more. Throughout the first three seasons he often complained about Penny hanging around them since she didn't have much, if any, of the same interests. After a scare that she might stop hanging out with them late in the third season he admitted that he had come to enjoy her presense. In Season 5 he also began pushing against the boundaries of his regimented life more often and admitted that his life didn't fall apart as a result.
 * Amy started off in the series as a straight Distaff Counterpart to Sheldon, having no sexual impulses, is condescending to others and even speaking in a similar manner with a dry wit. She started to show an interest in social activities with Penny and Bernadette and now considers Penny to be her "bestie" (best friend). By the beginning of the fifth season she still has a little of the Sheldon-esque weirdness about her but is otherwise a very social and friendly individual who knows how to have fun.
 * Characterization Marches On:
 * In the first episode Sheldon was basically just Leonard's even more geeky roommate with a dry sense of humor, although he still largely had the same quirks and qualities that have come to define him. The first episode has the "his spot on the couch" gag and he criticized Leonard's board of equations. But he seemed to be more socially astute (recognizing Leonard's crush on Penny and his chances with her) and not completely asexual (he appreciated the attention Penny gave him and was described as a "semi-pro" when at a sperm bank). It wasn't until the second episode that his arrogance and social ineptitude took hold (where Leonard had to make a "sarcasm" sign for him).
 * Similarly, Penny was a lot dumber initially (for example, claiming her screenplay isn't based on her life because she's from Omaha not Lincoln). She quickly moved from The Ditz to Closer to Earth.
 * Bernadette originally was unable to understand jokes and sometimes even sarcasm, though this might be a bit of Character Development as she gradually started explaining when something was a joke. Its later implied she was simply Obsfuscating Stupidity.
 * Chekhov's Gag: The Object Ceiling Cling in "The Classified Materials Turbulence"
 * Chewbacca Defense: Sheldon frequently employs this. See main entry for examples.
 * The Chick:
 * In most episodes, Penny is the token female, and as often as not, she acts the part. (Occasionally subverted, as when she kills cockroaches for the guys. In such situations, one or more of the guys will take on the role of The Chick.)
 * Although she's a chick, Leslie Winkle is almost never The Chick. Whenever she makes an appearance, at least one of the guys turns into The Chick. She lampshades this when attempting a relationship with Leonard "I believe you should take on the male role."
 * Closer to Earth:
 * Almost any of the female characters who appear on the show, but Penny most of all.
 * Also, Leonard compared with the other guys.
 * Most female characters are Closer to Earth than the four guys. Leslie Winkle, however, is more on a par with Wolowitz, Koothrappali and all the other 'average' nerds. Which makes her Closer to Earth than Sheldon, but much further from Earth than Leonard.
 * And then there's Amy, who is about as far out as Sheldon.
 * Closet Geek: Penny increasingly becomes this as the Series progresses. For example, Penny saw the new Star Trek movie alone and of her own accord while the guys were away in the Arctic.
 * Cloudcuckoolander: Raj is a bit like this, and the trait seems to be more prominent in more recent episodes.
 * Sheldon is basically on another planet as far as social norms are concerned.
 * Its revealed in "The Werewolf Transformation" that Sheldon believes that Barbers keep "Haircut records".
 * Clueless Chick Magnet: Sheldon has gained not one but two devoted groupies. As well, he ignores a girl who actually goes into his room and sits on his bed, and unwittingly manages to pick up a gay man.
 * After Sheldon ends up charming Raj's date (a successful dentist) causing her to leave for the date with him instead, he then completely fails to understand why he would see her again? He already has a dentist!
 * The Cobbler's Children Have No Shoes: Leonard's mother Beverley is a professional psychiatrist, but she has a very distant and unemotional relationship with her own children, having apparently treated them more like long-term test subjects than a family.
 * Cold Open: Every episode, although some use the rotating electron diagram and whoosh noise before starting.
 * Comically Missing the Point:
 * Sheldon with most social interaction, but a notable example that doesn't quite fit into that category:

"Sheldon: "I brought you some gummy bears." Penny: (confused) "...thanks?" Sheldon: "Now that you are in my debt, could you...""
 * A hurricane of them in "The Plimpton Situation", when Leonard tries to hint to Howard and Raj that he was up all night with the titular scientist.
 * Comically Small Bribe:

"Sheldon: (wearing an all-white, long tailed, frilly collared tuxedo) [when Penny says "no"] I don't understand why, anything after this is just going to look silly. [next shot of Sheldon wearing a classy, sharp black-on-black suit] I look like a clown."
 * Continuity Nod: Sheldon's explanation for "his spot" on the couch used in the pilot is repeated at several other times, once verbatim by Penny when Bernadette first joins the group. In the Flash Back in late season three Sheldon's explanation for his original spot, using a lawn chair, was identical except that it discouraged communication in a group, reflecting how far he had come socially.
 * Other nods are used as brief moments, one in particular being when Howard crashed the Mars Rover
 * One episode involves Sheldon going to court due to his bad driving when helping Penny in "The Adhesive Duck Deficiency".
 * The first episode mentions Joyce Kim and the transvestite neighbor, who both show up in the flashback episode.
 * The episode "The Hawking Excitation" mentions Sheldon's restraining orders from Leonard Nimoy and Stan Lee.
 * After buying a replica of Longclaw in "The Russian Rocket Reaction" its shown from thereafter to be hung up on the wall of the apartment.
 * Conversational Troping: Generally on sci-fi and comic book conventions, including things like a Five-Man Band.
 * Cool Big Sis: Penny ends up being like this to the others, a normal person who helps them with fashion and relationship issues, lampshaded with a discussion with Sheldon where this is played more literally when she talks him into letting her cut his hair.
 * Costume Test Montage: Penny takes Sheldon to get a new suit that should give him confidence for his awards banquet.

"Sheldon: In here, you’ll find emergency provisions. An eight-day supply of food and water, a crossbow, season two of Star Trek: The Original Series on a high-density flash drive. Sheldon: I have a pre-packed emergency 48 hour survival kit recommended by the Department of Homeland Security... and Sarah Connor."
 * The Couch: Leonard and Sheldon's couch in their apartment. Just look at the picture above.
 * Cow Tools: You could spend forever looking at Leonard and Sheldon's apartment and the comic book store and see all sorts of geeky collectibles. You can also make out computer manuals and software cases in their bookshelves.
 * Crazy Cat Man: Briefly. After a falling out with Amy in which he terminated his relationship with her, Sheldon buys 25 cats.
 * Crazy Prepared:

""I don't want to go back to India! It's hot, and it's loud, and there are so many people. You have no idea, they're everywhere!""
 * Creature of Habit: Sheldon, to the point where he views the most minor of changes in his life as The End of the World as We Know It.
 * Credits Gag/Freeze-Frame Bonus: The Chuck Lorre Productions logo and ensuing paragraph at the end of every show. Sometimes manages to get away with things the show probably wouldn't by virtue of the fact that nobody sees them on TV anyway. A complete list of them can be found here.
 * For example, the one at the end of the Age of Conan episode details Lorre's recent trip to Vegas and his imagining of a man going home and "blowing his brains out" after reflecting on his unsatisfying job.
 * Sometimes CBS' radar still manages to catch them, and they're blanked out when they actually air (but not on Lorre's web site).
 * Freeze-Frame Bonus also applies to the opening credits. Among other things, there is a TTC subway train, a 3-1/2" floppy disk, a disco ball, and a Hollywood Ave. street sign.
 * Cringe Comedy: Howard hitting on Summer Glau in the most obnoxious and creepy way possible. Poor girl.
 * Cultural Rebel: Rajesh is not too fond of Indian food, while Howard takes a perverse thrill from not keeping kosher.
 * Raj also can't seem to stand the idea of going home.

""Shrimp Caesar salad with no almonds for the highly allergic kosher-only-on-the-high-holidays Howard, and for our suddenly-back-on-the-Hindu-wagon Raj, meatlover’s pizza, no meat.""
 * Raj and Howard go back and forth on their respective cultures, as noted by Penny when predicting the guys' orders at The Cheesecake Factory in "The Panty Pinata Polarization"

"Howard: Winnie the Pooh is out of the honey tree!"
 * Sheldon is also one regarding his mother's religious lifestyle. He resents that he was forced to go through Cotillion, pointing out the lack of application that having all the social graces to be able to function in 18th Century Vienna presents.
 * Sheldon also affects an more upper-class accent, only slipping into his native Texan drawl when flabbergasted, irritated or angry.
 * The CSI Effect: Invoked; Sheldon expects too much of the police.
 * Cute Mute: Emily, a deaf girl that Raj dates.
 * Cutting the Knot: Penny has to get Sheldon's Flash drive from inside a puzzle box. Before he gives her the instructions on how to open it over the phone, Penny asks if he has any emotional attachment to the box. When Sheldon answers no, she simply smashes it open.
 * In another episode, Howard tries using a robot hand to pleasure himself. After Leonard and Rajesh run out of ideas of what to do, they take Howard to the Emergency Room. There, the Nurse suggests simply turning the hand off, and despite Howards pleas not to do so, she turns it off, and the hand lets go.

"Sheldon: "I can't do this." Leonard: "Are you kidding? You're a semi-pro!""
 * A Date with Rosie Palms:
 * In the first scene of the pilot, while Leonard and Sheldon are at a sperm bank to make donations for extra cash:

"Leonard: What's that? Howard: Your new girlfriend. You two have fun tonight."
 * Season 4 premiere. Hilarity Ensued.
 * When Leonard wonders how he can date someone who believes in psychics, Howard draws a diagram showing how few women will share his views, like him and be liked by him. When Leonard complains, Howard draws a dot on Leonard's palm.


 * Subverted in “The Love Car Displacement”: We see Raj, alone in his room, cheerfully step out of the bathroom with a box of tissues. He grabs two tissues and gets under the covers, shivers with anticipation and turns on the TV.

"Amy: And if the bar doesn't work out, we can always go to Walgreen's and get you a nice electric toothbrush. I call mine Gerard."
 * Female example with Amy:

"Howard: You mean playing D&D with us then taking a suspiciously long shower?"
 * Leonard muses that it's wonderful his girlfriend is 9000 miles away; he can do anything he wants.

"Amy: I think you might look sexy with long hair. Be the kind that flows down to your shoulders and blows back while riding on a horse. Bareback and barechested... I-I'm going to go brush my teeth, it might take a while."
 * Amy once again in "The Werewolf Transformation", musing on Sheldon growing his hair out.

"After you pass the first three barriers, you kind of want to take it all the way."
 * Deadpan Snarker:
 * Leslie Winkle.
 * Howard also took on this attribute more in later seasons.
 * The entire cast takes turns with this.
 * This is basically all Leonard does now since he got with Penny.
 * Just about anybody who has to deal with Sheldon becomes this at some point.
 * Sheldon was supposed to be this for Leonard in the pilot, but became a Breakout Character and was delegated to Butt Monkey instead. He still has moments of this despite not being able to understand sarcasm.
 * Penny, as she gradually became the Nerd Nanny.
 * Death Glare: Penny has one for Sheldon almost Once an Episode, though he rarely notices.
 * Penny did this to Raj in "The Skank Reflex Analysis."
 * Then Bernadette of all people took this trope Up to Eleven in the same episode.
 * Death Ray: Sheldon's mother or Sheldon has mentioned that Sheldon tried to build one as a kid but failed and thus they kept teasing him.
 * Pissed the dog off something terrible though.
 * Defcon Five: Leonard falls victim to this trope and is then lectured by Sheldon.
 * Defictionalization: The gang plays a card game called "Mystic Warlords of Ka'a" while a actual card release is planned the game can be played on Facebook
 * The Dev Team Thinks of Everything: When Sheldon's trying to learn to drive, the simulator he uses ends up allowing him to drive onto the second floor of a mall and then, with accurate whimpering, destroy a pet store.
 * Development Gag: In the season three special features the cast does a fortune cookie Q&A about their lives and favorite moments on the show, which looks to be ad libbed. Simon (Howard) makes a joke while reading a fortune cookie "Help, I'm trapped in a fortune cookie factory!" This same joke is referenced in the fourth season as a joke that Howard is always saying and trying to get a laugh from people.
 * Disabled Love Interest: The girl that Penny finds for Raj is deaf. So he can talk around her.
 * Disappeared Dad: Howard's father left when he was 11.
 * Disposable Sex Worker: A neighbour acted as one in CSI.
 * Discriminate and Switch: Stan Lee didn't put 'my friend' and 'Excelsior' when he gave Raj an autograph, and it would seem racist until Howard pointed out that that wouldn't be the case if Raj didn't bug him about his characters and their Alliterative Names.
 * Distaff Counterpart: Amy to Sheldon, for sheer longevity. Leonard's mom Beverly also possesses similar quirks, such as having a very particular way of having her tea.
 * Distracted by the Sexy: Whenever a new pretty girl shows up. Sheldon is immune, and, on occasion, so is Leonard. Howard is always the first to lose focus.
 * Subverted when they are focused on something else and the Sexy is verbal. Once, Penny and three friends stop by while they are playing Halo and ask if they want to have an orgy. After no response, Penny tells her friends "I told you so," and they leave. Shortly after, Leonard pauses the game and says he thought he heard something, but he shrugs it off. On another occasion the four guys are trying to come up with a better way to set up her entertainment system than the way suggested in the instructions and Penny attempts to get their attention by announcing that she was going to take all her clothes off, to no response.
 * The Ditz: Many of the female characters. Penny on occasion, especially in the first few episodes.
 * Does This Remind You of Anything?:
 * When Leonard and Penny are together several episodes deal with them as if they were a married couple with Sheldon as their child. It is heart-breaking.
 * In reference to the ordeal of becoming Sheldon's roommate in "The Staircase Implementation":

"Sheldon: I see, the humor is derived from..."
 * Leslie and Sheldon's argument about their respective theories in "The Codpiece Topology" was amusingly comparable to an argument over religious beliefs.
 * Dogged Nice Guy: Leonard. Less so during Season 3, but then he's finally with Penny.
 * Don't Explain the Joke: Yet another social convention Sheldon doesn't understand.

"Leonard: I'm starting to sense a Double Standard here..."
 * Double Standard: Leonard learns about these the hard way—after, Leonard attempts to do the same, once with Leslie and once with Penny. They're not pleased.

"Leonard: Awww no, not the pet store! Sheldon: Remind me to compliment Wolowitz on the software. The detail is remarkable."
 * Down on the Farm: Penny's from just outside of Omaha.
 * Drama Queen: Howard's mother is this. If she's not bugging Howard dramatically, she's getting dramatic about something else.
 * Drives Like Crazy: Penny does not actually drive badly, she drives like a person who has driven for a very long time and will sometimes bypass 'normal' behavior for a quicker route, such as not slowing down much over speed bumps. Her constant ignoring of the Check Engine light is a running gag, though.
 * Sheldon doesn't drive normally; part of the Roommate Agreement was that Leonard would take care of the driving. They eventually forced him to get a learner's permit but he will likely never get his license because even in a simulator he does horribly. In a later episode he had to drive Penny to hospital and while they got there in one piece, it wasn't a relaxing experience.
 * Driving Test: The gang try to teach Sheldon to drive using a computer simulation. He ends up driving through a virtual mall like in The Blues Brothers.

"Sheldon: I forgive you, let's go home."
 * Drop-In Character: Penny embodies this the most, as she has a tendency to stop by the guys' apartment for random reasons like coffee or tech support (Raj and Howard are usually over there for an actual activity like Halo night). On the other hand, Leonard often visits Penny in her apartment in not too dissimilar a manner, although often expressly because Penny needs someone to talk to. Penny does this so much that she will casually drop by the apartment in her sleep clothes, much to the displeasure of one of Leonard's girlfriends.
 * Dropped Glasses: and the inevitable Blind Without'Em, Leonard.
 * Dumb Blonde: Penny can be flighty at times, but overall she isn't stupid. The first couple of episodes she was more The Ditz but this was replaced with her generally being more Closer to Earth.
 * In one episode Penny takes some physics lessons from Sheldon so she could better understand Leonard and what he does. Although Sheldon is a horrible teacher, she does seem to learn a little, at least enough for a Techno Babble gag.
 * Dumb Is Good: Averted by the majority of Penny's boyfriends, who are dim and often rather obnoxious. Though played straight for Zach, who ends up befriending the guys and even enjoys their hobbies.
 * Dungeonmaster's Girlfriend: Not quite a girlfriend, Penny nevertheless occasionally attempts to get in on the nerd action.
 * Early Installment Weirdness: Sheldon is a lot more relaxed in the Pilot episode, and while droll he seemed mostly social capable. Compare to the Flash Back to when Leonard moved in from season 3, where Sheldon is much more socially awkward.
 * Many early episodes display Sheldon without traits that later become trademark actions, such as knocking on Penny's door once instead of thrice, and without stopping to say her name.
 * Easily Forgiven: Beginning of Season three. You know the one.

"Sheldon: Milk Dud? Zach: Oh I LOVE Milk Duds! ...okay, we're cool."
 * In "The Justice League Recombination" the guys have to apologize to Zach for making fun of him.

"Howard's mother: It's like tryin' to keep two dawgs in a bathtub!"
 * Egocentric Team Naming: Sheldon tries to get Leonard's app development team to name the app after himself, twice. The first time he uses an acronym and the second time he spells his name backwards. He claims both times it's a "happy accident".
 * In another episode the guys team up to help Sheldon get over his fear of public speaking, comparing themselves to the X-Men. Sheldon thinks that "since I am Sheldon Cooper, you shall be my C-Men."
 * Egopolis: Sheldon's SimCity he designed, Sheldonopolis. With architecture including Sheldon Square, Sheldon tower, Sheldon Stadium (home of the Fighting Sheldons), and Shel-Mart.
 * Eldritch Abomination: Not a straight example, but the painting of Penny and Amy from "The Rothman Disintegration" is hilariously treated as though it is one, by both Penny and Bernadette.
 * There is also Howard's mother who though never seen onscreen is described as an extremely obese, bald(ing) old woman who takes thirty minutes to climb three flights of stairs and needs help putting on dresses as she can't put her front and back in at the same time on her own.

"Leonard: You know all those terrible things bullies used to do to us? I get it."
 * Elmuh Fudd Syndwome: Wecuwwing Chawactuh Bawwy Kwipke.
 * Epic Fail: Exhibited by both Sheldon and Barry Kripke in their one-on-one basketball game to decide who gets the corner office in "The Rothman Disintegration." Leonard's comment while watching the "game" says it all:

"Penny: "A smart guy takes the nude photos of his wife off his cell phone before he tries to take nude photos of his girlfriend." Leonard: "He tried to take nude photos of you?" Penny: "That's what you took from that?! ...The guy is married!" Leonard: "Oh yeah. I'm uh... oh, that's terrible!""
 * Escalating War:
 * Between Raj and Sheldon in "The Hot Troll Deviation".
 * Between Penny and Sheldon when Penny finally had enough of Sheldon's insistent quirks, but it started largely because Penny got her "third strike" and Sheldon banished her from the apartment. Penny struck back by using up all the washing machines during Sheldon's laundry day, knowing how regimented his schedule is, but Sheldon has no boundaries he isn't willing to step over.
 * Even Bad Men Love Their Mamas: Sheldon's mom is the only one who can override Sheldon's irrational behavior.
 * While Sheldon loves his mom he still dislikes her religious zealot personality and is fine with jokes at her expense. When it comes to his "Memaw" (Grandma) he absolutely adores her.
 * Even Beggars Won't Choose It: When looking through Leonard's wardrobe, Penny picks out several shirts and tells Leonard to throw them away, noting that he shouldn't even give them to charity because: "Seriously, you won't be helping anyone."
 * Even the Subtitler Is Stumped: Howard is briefly stumped by Raj's Disabled Love Interest's fast and furious signing.
 * Everyone Knows Morse: Subverted in the episode "The Cooper-Nowitzki Theorem". Sheldon attempts to use Morse code; however, Leonard claims he doesn't know Morse code and refuses to learn it at three in the morning.
 * Everybody Remembers the Stripper: In-Universe this happens a few times. Once when Penny described a falling out with a recently acquired boyfriend.

"Amy: (all in one breath) "Sheldon and I engaged in sexual intercourse. In other news, I'm thinking of starting an herb garden. Mum's the word. Gotta go.""
 * Amy and Sheldon tried to do a social experiment to see which bits of juicy gossip would be passed quicker around their circle of friends. Being that they have little social skills, it was pretty obvious from the get-go their choice of subjects would render the experiment almost irrelevant.

"Sheldon: But I suppose it does take courage to demonstrate that kind of commitment to soup."
 * Cute Kitten: Sheldon's favorite childhood lullaby "Soft Kitty" proves you don't even need an actual kitten for this trope.
 * Sheldon does not, however, enjoy LOLcats; an email of such from Penny gave her her first strike.
 * Establishing Character Moment: The pilot gives a good moment to everyone;
 * Leonard's distracted look when seeing Penny in her apartment and subsequently trying to talk to her
 * Sheldon being more interested in the DVD Commentary of Battlestar Galactica than talking to their new neighbour
 * Howard trying to flaunt his Omniglot nature to Penny
 * Raj when Penny tries talking to him and he just keeps eating his meal as though she didn't say anything
 * Penny when she hugs Leonard and Sheldon and offers to buy them dinner
 * From the rest of the Series;
 * Leonard's mother and her constant psycho-analysing. Capable of reducing Penny to a flood of tears in the space of three flights of stairs... twice.
 * Embarrassing Tattoo: Penny has one she claims is the Chinese symbol for "Courage". According to Sheldon, it actually means "Soup".

""Did you have to make me sound like a Simpsons character!""
 * Establishing Series Moment: The "Sarcasm Sign" of the second episode
 * Everything Is Racist: ...to Rajesh

"Leonard: Let me try one! Calling Mcflono Mcfloonyloo! Cell phone: Calling... Rajesh Koothrappali. Rajesh: Impressive! ...and a little racist."
 * You kind of have to agree with him about the cell phone voice recognition software.

""That's more like: We're tall thin women who want to make a coat out of your Dalmatians.""
 * Everything's Better with Monkeys: Amy is shown owning a cigar-smoking capuchin monkey in the episode "The Agreement Dissection". Although, to quote her, he's a bit of an ass.
 * Evil Counterpart: Late in the second season a new neighbor moved in above Leonard and Sheldon, Alicia. She is pretty, blonde, an actress and very quickly acquires the attention of the guys, much like when Penny moved in. The main difference is that Alicia was a shameless flirt and manipulated the guys to do everything for her. While Penny did many similar things, she generally treated them with respect and didn't abuse them. Partially out of jealousy and partially out of concern for her guys, Penny eventually clashes with Alicia.
 * Evil Genius: Sheldon occasionally invokes this on purpose (see Evil Gloating and Evil Laugh below). Leonard has already noted that Sheldon's "one lab accident away from becoming a supervillain".
 * Later, when Leonard states that he's worried about Sheldon, Howard says "So am I. I'm worried that one day, he'll set off a low-yield nuclear device because the cafeteria ran out of lime Jell-O."
 * Evil Gloating: "Hello, Kripke. This classic prank has been brought to you by the malevolent mind of Sheldon Cooper."
 * "Hello puny insects!"
 * Evil Laugh:
 * Sheldon has a rather droll example.
 * Raj's laugh in "The Bat Jar Conjecture".

"Leonard: What would you be if you were attached to another object by an inclined plane, wrapped helically around an axis? Sheldon: Screwed. Leonard: There you go."
 * Evolutionary Levels: Invoked by Sheldon to explain why he shouldn't have to learn to drive. One of the many indications that Sheldon isn't the Omnidisciplinary Scientist that he thinks he is.
 * Expospeak Gag: Sheldon's "I'm polymerized tree sap and you're an inorganic adhesive, so whatever verbal projectile you launch in my direction is reflected off of me, returns to its original trajectory and adheres to you." And this is just one of many instances.
 * Sheldon's attempt at 'trash talk': "I am given to understand that you mother is rather overweight. Of course, if this is the result of a glandular problem and not over-eating, I will gladly retract my statement."
 * Not to mention this gem from "The Desperation Emanation":

F-J
"Sheldon: I'm in favor of anything that tries to replace actual human contact."
 * Facebook: The others are surpised Sheldon uses the website.

"Sheldon: It was a humorous conceit on the violation of the fourth wall and I did NOT care for it."
 * Fake Buzz: In one episode Raj starts hitting on Summer Glau (and skillfully at that), until Howard points out the beer was non-alcoholic, and he can't continue.
 * Fake Crossover: The Late Late Show with Craig Ferguson did a Cold Opening where he was applying to be friends with the group, filled with quite a few character bits (Raj didn't like his accent) and Self-Deprecation. Craig later interviewed Johnny Galecki that same night.

"Sheldon: If you fail at this relationship, and history suggests you will, then we risk losing the medical officer our landing party has always needed. Leonard: What landing party? Sheldon: You're Kirk, I'm Spock, Wolowitz is Scotty, Koothrappali is the guy who always gets killed [looking at Leonard's doctor girlfriend at the time] and now we've got McCoy."
 * Fast-Forward Gag: Played with; when the main characters buy a Time Machine replica, they pretend they're moving in fast forward.
 * Fate Worse Than Death: In a purely silly sense, it's taking care of Sheldon when he's sick, or if someone aside from Leonard drives him to work.
 * Or sits in his spot or changes his schedule...
 * Fawlty Towers Plot: Subverted in an episode where the lie works perfectly, but Sheldon overcomplicates it when he notices minute flaws in it. The lie never actually falls apart.
 * Also subverted in "The Recombination Hypothesis" Leonard ended up having to explain to Sheldon why he was returning to the apartment at 3 in the morning, when Sheldon was getting out of the bathroom. The real reason was but Leonard didn't want to tell Sheldon about it. So it slowly got more and more implausible as Sheldon poked holes into the explanation, until Leonard actually had some evidence to back up his claim (an asthma inhaler brought up in the previous scene).
 * First Kiss: Sheldon gets one from a drunken Amy. It's mostly awkward for both of them.
 * Sheldon received one earlier from a drunk Mrs. Hoffstader. No one really wants to talk about it after the fact.
 * Five-Man Band: Done through Conversational Troping, Sheldon has grouped the cast into his own Star Trek-based version and crossing over into the Command Roster.

"Leonard: This one is particularly disturbing."
 * Sheldon also determined the four guys' roles in a Four Man Band. He is "the smart one", Howard is "the funny one", Raj is the "lovable foreigner who struggles to understand our ways and fails", and therefore Leonard is "the muscle" by default.
 * Flanderization: The local Comic Book Store owner, Stuart, was originally just a very normal guy who successfully asked Penny out. It was a key plot point that in terms of being a decent, normal guy he was virtually identical to Leonard. While he remained a friendly guy he later gained some neurotic ticks, low self-esteem and has a lot more trouble talking to women than before. The change can probably be explained that "nice, normal guy" doesn't leave things too open for comedy and they wanted him to stand apart from Leonard.
 * An inversion of this trope is done in the Whole-Episode Flashback to when Leonard and Sheldon first met. The Sheldon of the series has all sorts of quirks but still makes awkward attempts at social interaction and understanding how normal people think, the Sheldon of the Flash Back was basically a flanderization of his current personality where his Control Freak and Insufferable Genius mannerisms were about all he was. While not really elaborated upon, it's suggested that being friends with Leonard is the reason Sheldon of today is even remotely workable.
 * Fleeting Passionate Hobbies: Sheldon after losing his job. One of them has him at a loom.

"Raj: "I still wear mine when there's a nip in the air.""
 * Brought back in season 4, Leonard does say that he got good at it and made them matching serapes.

"Leonard: You put ground-up moth in my food?! Sheldon: For Science!!"
 * Flipping the Bird: Played with. After Sheldon made an insult about Wolowitz's robotic arm, he gave it a command and it held up the peace sign, which confused Sheldon and Howard tries fixing the code.
 * Sheldon once quoted Shakespeare to Penny about how she made him miss an Autograph signing with Stan Lee, making dramatic poses with his index finger in the air. When he left the room Penny felt like he gave her the finger in some way.
 * Food and Animal Attraction: In one episode, Sheldon is chased by a vicious dog because it can smell the hot dogs Sheldon was hiding in his pants.
 * Foot Focus:
 * In general, Penny Does Not Like Shoes except for flip-flops.
 * Although a point is often made about how many shoes she buys, she never actually seems to wear them.
 * The episode explaining how Leonard and Sheldon met had this in the present day sequences.
 * For Science!

"Raj (amused): You’d think it’s because my parents didn’t love me, but actually they loved me a great deal."
 * Freaky Fashion, Mild Mind: Alice from "Good Guy Fluxuation" was a female geek (very rare on the show) and dressed in a combination of punk rocker and goth, along with a noticeable tattoo on her chest and a wide assortment of piercings. She turned out to be really friendly and well-mannered in addition to her geeky passions.
 * Freeze-Frame Bonus: Howard's mother, never actually seen before on the show, can be seen from above in the zoom out from Howard's wedding in the Season 5 Finale.
 * Freudian Excuse: Averted by Raj, when he decides to be a douche for no apparent reason on the penultimate episode of season 4.

"Sheldon: Are you and Leonard "Friends With Benefits?" Penny: No! Did he say we were? Sheldon: Leonard said nothing, but who knows what goes on over here when he pretends your mail was misdelivered. Penny: What? Just mail, no benefits."
 * The reason why Leonard is so needy in relationships, likely comes from the fact that his mother maintains a cold detachment from him and treats him as more like a test-subject. His need for intimacy resulted in him building a hugging machine as a child.
 * Freudian Trio: Confirmed by Word of God, the Penny/Leonard/Sheldon relationship was designed to be like this. Sheldon is The Spock, who represents "logic" and the aspirations of science over all else. Penny is The McCoy, who represents "emotion" and the promise of a full life to experience. Leonard is The Kirk, who is torn between those two worlds.
 * Amy incidently describes the trope when depressed and analyzing her relationship with Bernadette and Penny, but done in her own neurobiology terms. Penny is the creative and spontaneous right half of the brain while Bernadette is the scientific and analytical other half. Amy is the one of the group caught between the two halves, but her comparison comes out to her being a tumor.
 * The Friend Nobody Likes: Sheldon frequently takes this role.
 * Barry Kripke.
 * Friends Rent Control: It's not as bad as it could be, since they aren't living in a luxury New York suite, but a smaller building with a broken elevator in Pasadena. Sheldon mentions that if he could afford it he wouldn't have Leonard as a roommate. Penny seems to mostly afford her apartment on a waitress paycheck (and tips) with little trouble, at least until it's plot relevant. Unlike other examples of this trope, rent issues are relatively common. Penny has had to leave work from time to time because of the guys, and she always points out that losing a day's pay is not helpful.
 * It might have more to do with the fact he needs Leonard to drive him to work than to pay for the apartment. He seems to have more than enough money as he doesn't cash his paychecks.
 * Friends with Benefits: Discussed, with Sheldon not really understanding the concept. "What exactly does that expression mean, 'Friends with Benefits?' Does he provide her with health insurance?"

""Suprisingly Helpful Equation Link Differential Optimise Numerator""
 * Friendship Moment: With regularity. They like to prank each other and often don't get along, but all the guys came from the geek end of the social pool and so they've banded together really tight. Sheldon, in particular, did not have many friends growing up and when the moment comes he is very grateful for the friends he has. This happened as early as the second episode, where Penny freaked out over a violation of privacy (Sheldon cleaned her apartment while she was sleeping). After thinking it over she forgave them, and even told Leonard everything was okay when he came over to apologize.
 * Full-Name Basis: Amy is often referred to by her full name, Amy Farrah Fowler.
 * Fun T-Shirt: There's even a website that keeps track of the characters' shirts and where you can buy them. In one episode, a gag was about Raj having a shirt with a speaker built into it. It could play everything from the Imperial March to the Final Jeopardy theme. You can get it here.
 * Fun with Acronyms: In "The Bat Jar Conjecture" the guys decide to enter the university's Physics Bowl and have a debate on what to name their team. Sheldon prefers the Army Ants while Howard suggests Perpetual Motion Squad. Later, Sheldon has a fallout with the others and actually enters the Physics Bowl against them... so it's AA vs. PMS.
 * Sheldon's suggestion for the name of Leonard's iPhone app.

"Penny: (As Sheldon tries to leave for his bedroom) Wait, wait! Sheldon, come back! You forgot something! Sheldon: What? Penny: This plasma grenade! (Sound of large explosion) Ha! Look! It's raining YOU!"
 * Fun with Subtitles: Howard knows sign language. He's a terribly lazy translator.
 * Gamer Chick: Penny isn't a gamer, but in S1 Ep07, "The Dumpling Paradox", she fills in for Howard for the guys' Halo night, and the first time she picks up an Xbox controller, she manages to outclass all of them on her first try. And yes, the guys are 30-year-old geeks who play Halo religiously. However, considering Penny's more rounded characterization, this is surely less Positive Discrimination and more Rule of Funny.

"Sheldon: I don't know how, but she is cheating. Nobody can be that attractive and this skilled at a video game."
 * Sheldon clearly doesn't believe in this trope.

"Sheldon: "I still don't understand why no one else bid on the (what he thinks is a minature) time machine". (Switch to the foursome standing around the recently delivered full-size time machine) "I understand why no one else bid on the time machine.""
 * S2 Ep03, "The Barbarian Sublimation," also has Penny getting addicted to Age of Conan.
 * Geek Physique: Both Sheldon and Howard are very skinny, and once Howard boasted of having 3% body fat (described by Raj as a "Human Chicken Wing"). Raj and Leonard are of average size (though there is a reason we rarely see Leonard barechested or in simple t-shirts, as Johnny Galecki is in pretty good shape). The only "geek" on the show who is overweight is the minor background character "Captain Sweatpants."
 * Geek Reference Pool: Averted. Their pool runs deep, although they seldom leave it.
 * Geeky Analogy: Most explanations of anything involving social conventions.
 * Geeky Turn On: To be expected given the premise of the show. One episode had Raj and Sheldon together with Sheldon holding a Green Lantern Power Battery and it actually attracted the attention of a couple of girls, thinking it was cool. An unfortunate side-effect of this trope shows up when
 * When dating, Penny suggested that she and Leonard make out on Sheldon's spot on the couch. This was seen as quite a taboo thing to do.
 * Genre Savvy: Penny manipulates Sheldon into re-rolling dice by pointing out "Doubles. Roll again."
 * Gilligan Cut: The Nerdvana Annihilation

"Leonard: Whoa, its a little early to be dropping J-Bombs, don't you think?"
 * Girlfriend in Canada: Amy Farrah Fowler admits she once told her family she had a boyfriend who was a miniature horse breeder. The lie unravelled when she was asked were they met. She panicked and said "Woodstock".
 * Girl-On-Girl Is Hot: Averted, when a very tipsy Amy gave Penny a mouth kiss ("Come here, Bestie, give me some sugar") it was not only very underplayed but Penny even gave an embarrassed laugh after it happened. In addition, there wasn't any rising laughter by the Laugh Track.
 * A similarly understated moment happens when Penny and Bernadette discuss the awkward things Amy likes to talk about with them such as painting fertility symbols on Bernadette's naked body as being a wedding ritual. The guys noticeably quiet down after they say that, with Raj in particular (being silent anyway) subtly staring off into space.
 * Give Geeks a Chance
 * Gold Digger: Raj's Disabled Love Interest lets him shower her with many, many gifts. Penny also muses that Raj is hotter now that she knows he's rich.
 * Gone Horribly Right: The foam in Kripke's office was supposed to be a prank on just Kripke, Sheldon didn't expect it to fall on the president of the university and the board of directors.
 * Good Is Not Nice:
 * Very much Depending on the Writer, Sheldon. He's sometimes bad, sometimes good, and very rarely nice.
 * And Leonard, starting at the end of season two and well into season three with  for example.
 * Also Penny & Howard can be pretty mean at times.
 * Goofy Print Underwear: On one episode Howard talks Leonard and Raj into being his wingman at a bar. They all change out of their standard Superhero symbol boxer shorts .... just in case.
 * Gosh Darn It to Heck: Sheldon when drunk at Howard's bachelor party starts saying "Jeepers!".

"Sheldon: Oh gravity thou art a heartless bitch."
 * Gravity Is a Harsh Mistress: Almost mentioned by name.

"Amy: If your friends are unconvincing, this year’s donations might go... say, the geology department. Sheldon: Oh dear, not the dirt people! Amy: Or worse, it could go to... the liberal arts. Sheldon: No. Amy: Millions of dollars being showered on poets, literary theorists and students of gender studies. Sheldon: Oh, the Humanities!"
 * Gray and Grey Morality: In "The Speckerman Recurrence," Penny, Bernadette and Amy have a change of heart after nearly taking clothes from a donation bin.
 * Groin Attack: Sheldon's sister's method of keeping Sheldon in line.
 * Penny administers one to the guy who hacked Sheldon's World of Warcraft account in "The Zarnecki Incursion".
 * Howard sets Leonard up with a date that knows 100 ways to rip a guy's nuts off. She's not shy about demonstrating them in a restaurant.
 * Hair Today, Gone Tomorrow: In the flashback episode late in season three, Leonard had long, wavy locks, Howard had a Jewish Afro and Raj had something of a mullet. Sheldon was the only one with the same hair-style, and with the exception of Howard their current looks are big improvements.
 * Halloween Cosplay: The group, plus Penny's then-current boyfriend dress up as the Justice League of America for a costume contest
 * Hard on Soft Science

"Sheldon: Why is Leonard softly banging his head against his bedroom door?"
 * Head Desk:

"Raj (to Howard): Last night I had a dream, we got so rich from the app we made, you and I bought matching side by side mansions. But, there was a secret tunnel connecting your front yard to my back yard. What do you think it means? Howard: It means next time we play squash I'm showering at home."
 * Heartbreak and Ice Cream: Raj Book Ends a brief relationship with a Disabled Love Interest by comforting himself first with pie then with cheesecake.
 * In one early episode Penny is seen eating an entire tub of ice cream while crying her eyes out due to a breakup.
 * Heel Face Turn:
 * In "The Russian Rocket Reaction," one of Sheldon's mortal enemies crosses himself off of Sheldon's list.
 * Helium Speech: Kripke fills Sheldon's office with helium while the latter is on call for an NPR interview. The pitch of his voice increases throughout the entire interview.
 * Her Codename Was Mary Sue: The episode where Penny becomes addicted to Age of Conan everyone's characters were clearly named after them: Sheldon was Sheldor (The Conqueror), Penny was (Queen) Penelope and Howard was... Sir Howard of Wolowitz.
 * Heroic Blue Screen of Death: Sheldon when he discovers that Leonard, Howard and Raj lied to him about the results of his experiments at the North Pole after he has already boasted about changing the face of physics to everyone, earning him a ton of ridicule when he has to print a retraction.
 * Then Penny's attempt to cheer him up, by comparing his situation to when Young Spock was teased for being half-Vulcan, leave him in further despair when he discovers even she has seen Star Trek before him.
 * Heroic Sacrifice: Sheldon in "The Skank Reflex Hypothesis."
 * Heterosexual Life Partners: Howard and Raj argue like a married couple, and are generally paired together in team activities and usually serve as each others "wingman." Leonard and Sheldon are a more mild version, as Leonard can only stand Sheldon for limited periods of time.
 * Hidden Depths: Sheldon proves to be surprisingly understanding and helpful when hearing about his friends' love problems.
 * Hilarious Outtakes: You can only imagine the slip-ups that occur due to all of the terminology the characters throw around. Jim Parsons in particular had no end of trouble with the "Rock, Paper, Scissors, Lizard, Spock" explanation, just by the sheer length, the hand motions, timing and not letting the audience laughter throw him off.
 * Hilariously Abusive Childhood: Sheldon. Also Leonard, to a degree.
 * Hollywood Dateless: We are supposed to believe Leonard is awkward with women, and in a way he is. However, his dating history includes many hot women - Penny, Dr. Stephanie, the Korean spy, Leslie and now Priya - so one has to wonder why would he think he is unlucky with women.
 * Also part of his rather obvious Character Development during the show is that he gets better around women thanks to spending time with Penny. Same with Howard. Averted with Raj, who still can't speak to women who aren't relatives without drugs.
 * Hollywood Nerd: Type 1 is first played straight in the pilot where Leonard pines after Penny, and he and Sheldon get bullied and humiliated trying to get her TV back from her stereotypically Jerk Jock ex-boyfriend. Later, we learn that scientists, academics, comic book geeks, and Wil Wheaton are perfectly capable of picking on each other without outside help.
 * Type 2. None of the four main guys are particularly bad looking, but Leonard, played by Johnny Galecki, is the most prominent example. Are we really supposed to believe this guy is a nerd who has trouble with the ladies?
 * Hollywood Pudgy: Poked at when the guys managed to convince Penny and her date Zach to join them at a costume party as the Justice League of America. Penny got upset over things both overt and subtle and refused to go, and Sheldon tried to convince her to come by claiming to know why she was upset... that she thought she looked fat in the Wonder Woman costume. That was obviously not the reason she was upset (and clearly not the case in the show) but Penny then started to worry that maybe she did look fat... and Sheldon tried to "comfort" her saying it doesn't matter since Amazons were supposed to be "beefy gals."
 * Invoked again by Sheldon when, after Penny takes the last dumpling, supposedly one reserved for a guest of honor, he curtly tells her, "I've seen your mother. Keep eating." The downcast look on Penny's face says she really took that one to heart.
 * Averted as practically the poster child for the trope, Sara Rue, guest starred in a short story arc in season two as a Love Interest for Leonard (and briefly Howard). She is depicted as being exceptionally attractive and that Leonard was lucky to have her.
 * Homoerotic Subtext:
 * Lots—A disproportionate amount is between Rajesh and Howard. In Leonard's case, it often borders on Foe Yay, as when he describes one of Penny's boyfriends as "dreamy."
 * One episode featured a dream of Sheldon's where Wolowitz and Raj had stopped holding desperately to the Ring of Power, and were instead holding each other.
 * How about this gem?

"Raj: Really? What was I doing to your neck last night while playing Xbox?"
 * Leonard's mother has never been wrong about anything in her psychiatric evaluations of the cast, therefore her ideas about Howard and Raj must be correct as well.
 * There's also some between Amy Farrah Fowler and Penny. For example, in "The 21-Second Excitation", Amy thinks that at slumber parties, girls often experiment with lesbianism, and tries it on Penny. It is increasingly overt as she makes references to Penny's bosom defying the laws of physics and brings up "bridesmaid traditions" that involve stripping down and washing each other.
 * This goes all the way into the DVD Special Features. In "Set Tour with Simon and Kunal" they talk about how the stairway set doesn't have much space down below, forcing them to cuddle close to not appear on camera (complete with demonstration). And when the two find Johnny Galecki in the main apartment set, they end up snuggling together while asleep.
 * Taken to ridiculous lengths in the second episode of season 5 when Raj and Howard use a simulator to make out with each other.
 * Later in season 5, Howard mentions that he can't imagine receiving a massage from another man.

"Leonard: Yeah, sorry. I forgot about all of that. Raj: But I never will."
 * Leonard ends up taking Raj to Switzerland on Valentine's day, who squees at discovering the champagne and chocolates meant for Penny.

"Katee Sackhoff: Howard, do you have latent homesexual tendencies? Howard: Of course not! George Takei: So you say... yet here I am!"
 * Howard in one of his masturbation fantasies imagines Katee Sackhoff, Bernadette... and George Takei.

"Leonard: Sheldon, you can't be selfish. We all paid for it so it belongs to all of us. Now get out of the way so I can sit in my time machine."
 * Honey Trap: As found out through flashbacks, Joyce Kim.
 * Hot Mom: Apparently, what Dr. Gablehauser thinks of Sheldon's mother... and so does Howard.
 * Sheldon and Leonard's mom, although on a purely mental level. Sheldon even keeps in touch with her, to the point that he knows things Leonard is surprised by.
 * Raj's mother is a more classical example.
 * Humorless Aliens: Frequently referenced when people call Sheldon an alien, ask what planet he's from, etc.
 * Hypocritical Humor:

"Raj: "You are always so nice to me." Bernadette: "I'M NICE TO EVERYONE!!!""
 * While she is normally very sweet and bubbly, Bernadette once raked Raj over the coals for implying there was something between them and you can't help but notice the irony in this statement:

"Raj: Some of it makes sense and some of it is crazy, the point is I forbid you to date Leonard!"
 * Sheldon once claimed that Barry Kripke "lacks the basic social skills that we take for granted". He also accused Leonard of having Narcissistic Personality Disorder.
 * When on a "non-date" as friends hanging out, Leonard and Penny argued over the things they hated doing together (Leonard doing karaoke at 2AM and Penny watching a documentary). But when trying to strike up a conversation with other people, they used those same things to make themselves seem more interesting.
 * When Sheldon points out that Hindu customs mean that Raj does get to say who Priya dates. Also that by disobeying it, she'd be "reborn as a jackal with many diseases". She counters that by eating beef, Raj would have to "live with a cow for several months and drink their urine".

"Howard: "DO YOU REALLY THINK YOUR LIPS IN MY EAR IS HELPING???""
 * I Have This Friend: While Penny admits it's her own story, she tells Sheldon in "The Flaming Spittoon Acquisition" about how she never took the chance to tell a guy about her feelings for him until it was too late. It's fairly obvious to the audience she was talking about Leonard (the episode even shows her with signs of depression by drinking excessively) but Sheldon mistakes "the guy" she liked as being him, which she corrects him for.
 * I Know Mortal Kombat: Scattered around various episodes are claims of knowing how to perform a certain sport by practicing with video games. Sometimes not even that, Sheldon claims to know how to swim by practicing in the living room.
 * The "I Love You" Stigma: In a moment in bed, Penny quotes The Empire Strikes Back and Leonard told her he loved her. This led to a great deal of awkwardness because Penny wasn't expecting that and knew Leonard was waiting for a reply...
 * I Owe You My Life:, the main reason Leonard lets Sheldon get away with as many demands as he does.
 * I Resemble That Remark: When Leonard's mother claimed that Howard and Raj were in an "ersatz homosexual marriage", they are bothered by this... and instantly start arguing the point Like an Old Married Couple.

"Penny: Howard, you're going to throw away a great girl like Bernadette just because you're holding for some ridiculous fantasy? Howard: Hey, just because you settled doesn't mean I have to. Leonard: Excuse me, I'm sitting here. Penny: Hey, I didn't settle for Leonard. I mean, obviously he isn't the kind of guy I usually go out with. You know, physically. Leonard: Again, I'm right here! Penny: My point is, I do not judge a book by its cover. I'm interested in the person underneath. Leonard: (To Sheldon) I am here, right? You see me."
 * When Penny and Leonard had a fight, Sheldon goes to Penny to try and rectify the situation, only to end up confessing to her that Leonard is highly annoyed by some of her habits but has never told her because, according to Leonard, Penny "is overly sensitive and has a temper". Penny's response is to tell Sheldon to tell Leonard to drop dead.
 * Howard often responds to his mother's treating him like a child by reminding her that he is 26 years old. Followed by agreeing for her to bring him a popsicle.
 * I Take Offense to That Last One:
 * Subverted, when playing a 20 Questions game Raj managed to guess Leonard's item of C-3PO by saying "Does he look like a shiny Sheldon?" Sheldon perks up as Raj guesses correctly and appears at first miffed, only to say that he is flattered but doesn't see the resemblence.
 * In defense of having Amy around Sheldon once listed off all the things he had to silently put up with having Penny around. Leonard didn't argue any of the things listed, but got rather upset with the "silently" part.
 * I Think You Broke Him: In one episode, Penny is giving Sheldon acting lessons, and they are acting out a play Sheldon wrote when he was 10. He is acting as his mother, and begins to improvise, relating it to his real life. When he breaks down and starts crying, Penny calls up his mother and says, "Mrs. Cooper? Hey, it's Penny. Yeah, I think I broke your son," and hands the phone to Sheldon. "Mommy I love you!"
 * I Want My Beloved to Be Happy:
 * Penny breaking up with Leonard because she didn't want to hurt someone so vulnerable and inexperienced at long-term relationships. It was Wil Wheaton who planted the idea in her head just to win a bowling match, but that doesn't, necessarily, mean there wasn't truth in that reasoning.
 * Somewhere between this and Can't Spit It Out, Penny doesn't want Leonard to leave to go to the North Pole with the other guys but at that moment Leonard and Penny had no commitment to each other. She didn't want to interfere with his science projects and also wasn't ready to confess her feelings for him.
 * I Want You to Meet An Old Friend of Mine: There are several people on this show who also featured in Roseanne, first and foremost Johnny Galecki as Leonard. Sara Gilbert plays Leslie Winkle who briefly dates Leonard and Laurie Metcalf plays Sheldon's mom. Galecki also pointed out at a convention that his first kiss was with Mayim Bialik when he guest starred on Blossom years ago.
 * I Was Quite a Looker: Mrs. Wolowitz, apparently...
 * Idiosyncratic Episode Naming: Episodes are titled as theorems, postulates, conjectures, etc. And it is usually descriptive ie "The Nerdvanna Annihilation" involves Leonard contemplating selling his nerdy collection. Sometimes it's about something major to the plot, other times it's a throwaway line.
 * Idiot Ball: Leonard turned a non-date "hanging out" activity with Penny into an opportunity to confess to all the things that he let her get away with when they dated, generally acting very obnoxious and the evening turned into dirty laundry being aired out. Leonard later apologized for his behavior, only to learn except for the "dirty laundry" part Penny liked seeing him take charge and stand up for himself (showing signs of attraction to him). As they parted ways for the evening, he mused to himself "I am such an asthmatic dumbass."
 * I'm Standing Right Here:

"Sheldon: Please. Even assuming you could answer any question the way I would, the algorithms used by matchmaking sites are complete hokum. Howard: And that's exactly the answer we gave to the question, "What is your attitude towards online dating?" Raj: Howard wanted to write mumbo jumbo, but I said no, our Sheldon would say hokum."
 * Raj gives a silent one, when everyone went to bed and turned off the lights, forgetting Raj was still there.
 * Imagine Spot: The episode "The Recombination Hypothesis" has a big one,  Later at the end,
 * Leonard imagines how he could have handled a situation with Penny differently in "The Nerdvanna Annihilation" and has him become the hero by opening the elevator shaft and taking her down himself.
 * Raj has a series of daydreams about how Bernadette could leave Howard and they get together. Each one starts off normal only to progressively become weirder, culminating in a Bollywood dance number.
 * Improbably Predictable: In "The Lunar Excitation":

"(to Penny) Welcome to the Raj Mahal!"
 * In Soviet Russia, Trope Mocks You: "You don't screw the roommate agreement. The roommate agreement screws you!"
 * Incredibly Lame Pun: Raj is full of them.

"Missy: I am so proud to tell friends my brother's a rocket scientist. Sheldon: You tell them I'm a rocket scientist? I'm a theoretical physicist!"
 * Insane Troll Logic: Sheldon hates being wrong and when he can't refute something with normal logic he resolves to this trope to get his way, such as claiming to be a new evolution of mankind that are far more intelligent but incapable of driving properly.
 * It appears that Sheldon and Amy's made-up game "Counterfactuals" runs on this trope. For example, a question asks "In a world where mankind is ruled by a giant intelligent beaver, what food is no longer consumed?" The correct answer is "cheese danish" rather than "cinnamon" which is made of tree bark. They explain this as because of the Dams built to worship and appease the Beaver overlord, which would have left low-lying countries like Denmark completely flooded and thus deprived the world of it's namesake confectionary.
 * Insistent Terminology: Shows up from time to time, especially with Sheldon who prefers it when accurate terms are used. One of the more notable things he prefers is to refer to sexual intercourse as 'coitus', probably to separate it from sex as in 'male or female'. (Note: Coitus actually strictly refers to heterosexual intercourse in which a vagina is penetrated by a penis and nothing else so calling any other type of sex this is inaccurate).
 * Sheldon does not play "pranks"; he subjects people to his classic pranks.
 * Instant Expert:
 * A mild example: Penny, at computer games.
 * Sheldon often thinks he's this. His attempts at learning Mandarin met with failure.
 * Penny also beats Leonard at chess the first time she plays it.
 * Instant Web Hit: Penny Blossoms and the "fighting physicists" video.
 * Insufferable Genius: There's a reason why Sheldon is the page image.

"Leonard: Did I tell you that you'd have to make arrangements to get to work for the next few weeks? Sheldon: You did. Leonard: ...And? Sheldon: I didn't. [Beat, as Leonard collapses on the couch] Let's go!"
 * Interrupted Intimacy: Sheldon is quite happy to interrupt Leonard and whoever his partner is in the middle of the act- for example, with Joyce Kim. Sheldon decided to interrupt by knocking on the door. Leonard was thinking of ignoring him, but Sheldon knew he was being ignored. Sheldon then came in to remind Leonard of their Roommate Agreement. Due to its terms, Joyce decided to leave.
 * By definition, this happened with
 * Intoxication Ensues: Several examples.
 * "I drank milk that tasted funny."
 * Everyone (except Sheldon) in "The Adhesive Duck Deficiency" - Leonard, Howard and Raj through and Penny through painkillers.
 * Sheldon's diet virgin Cuba Libres "turned out to be kinda slutty."
 * TO LIFE! TO LIFE! L'CHAIM!
 * It Got Worse: see Evil Gloating.
 * It Will Never Catch On: "I assure you, you'll be sorry you wasted your money on an iPod when Microsoft comes out with theirs."
 * It's All About Me: Sheldon, thy vanity knows no bounds.

"Sheldon: YOU DID THIS, didn't you! Wil Wheaton: Do you really think I would break up a couple, just to win a bowling match? Sheldon: No... I suppose not. Wil Wheaton: Good. Keep thinking that. Sheldon: Wheeeeeatooooon!"
 * Amy is this about Howard and Bernadette's wedding. This goes so far as wearing her dress to City Hall complaining about her missed opportunity when the wedding might be put on hold.
 * Jerk with a Heart of Gold: Sheldon is this at times, particularly towards Penny.
 * Jerkass:
 * Of the five major characters, Sheldon.
 * Almost anyone who fits into a role as a Romantic False Lead, including most of Penny's boyfriends and hookups.
 * Leslie Winkle is this toward Sheldon.
 * Barry Kripke and many minor characters.
 * Wil Wheaton (at least, his character, not the man himself) for intentionally increasing the wedge between Penny and Leonard, just to get back at Sheldon.

"Leonard: You may be from Texas, but I'M from JERSEY!"
 * Jimmy Speckerman, who bullied Leonard in junior high. He gets drunk and apologizes but the following morning he demonstrates he's a Jerk with a Heart of Jerk.
 * Jewish Mother: Howard's.
 * Jews Love to Argue: Howard and his mother. A lot.
 * Joisey: Leonard is from NJ, which comes up from time to time. Sheldon boasts of his Texan upbringing as making him an expert at retribution, but Leonard manages to turn a prank back on Sheldon.


 * Just One More Level: Penny in "The Barbarian Sublimation".

K-O
"Raj: Leonard pretends to be a friend to Stuart, but instead is a two-faced bitch. Thus, he is reincarnated as a banana slug!"
 * Karma Houdini:
 * Lampshaded in the episode where Leonard meddles in Penny's date with Stuart.
 * Penny's ex boyfriend Kurt in the pilot and "The Financial Premability".
 * Killer Robot: "MONT-E" whom the guys built for a robot fighting competition.
 * Kissing Cousins: Howard and his cousin Jeannie, aparently.
 * Kryptonite-Proof Suit
 * Laser-Guided Karma: Raj invokes this when Leonard intentionally tries to screw up Stuart's date with Penny;

"Penny: I'm not talking to you! Zach: Then who are you talking to!? ...Babe?"
 * Late Arrival Spoiler: In trying to comfort Sheldon over a deception the others pulled on him while they spent three months at the North Pole, Penny referred to the '09 Star Trek film and explained a spoiler-heavy plot point as a comparison. Sheldon had not seen the movie yet. "I missed Comic-Con and the new Star Trek movie!"
 * Laugh Track: After every line, complete with pause, since it's the Studio Audience's actual laughter. People going to the tapings even say that they have to tone it down. Occasionally, you hear one laugh after the Techno Babble part of an Expospeak Gag and another when it's translated into Layman's Terms.
 * Sometimes though, when they want to show Sheldon sympathetic in episodes like "The Guitarist Amplification" or "The Bozeman Reaction" the laugh track pretty much hinders this.
 * It also leads to no end of people complaining about the laugh track and how fake it is.
 * Let's Get Dangerous: Sheldon, of all people, gets a moment like this in the penultimate episode of season three. It's revealed that the reason Leonard puts up with Sheldon is due to the fact that before the series began,  This is also why the elevator has not worked since the start of the show.
 * Like an Old Married Couple: Raj and Howard. Leonard and Sheldon count, too.
 * Lampshaded by Penny and Sheldon in season 5.
 * Heck, lampshaded by Leonard's mom somewhere in season 2 or 3, when she called it an "ersatz homosexual relationship" created to fill the void left by their repeated failures at maintaining heterosexual ones.
 * Like An Old Divorced Couple: The season 3 episode "The Spaghetti Catalyst", have Penny and Leonard having a passive-aggressive fight identical to that between two divorced parents squabbling over the custody rights for Sheldon. Leonard plays the long-suffering primary care giver, and Penny is the parent who drops in to take Sheldon to Disneyland.
 * Limited Social Circle: The four guys and the three girls. That's pretty much it. Even at Howard and Bernadette's wedding there were only two family members present, and evidently no other friends in the city who were worth inviting to the rooftop ceremony.
 * Limited Wardrobe: In a fun mix between this trope and Unlimited Wardrobe, everyone has a series of outfits that they rotate through. Sheldon has a Flash t-shirt that shows up often, Leonard has a jacket over a hoodie and brown pants he is always wearing, Raj is usually wearing a sweater-vest and Howard wearing uncomfortably tight turtlenecks and odd colored jeans. Penny has a wider variety, but her leisure clothing also tends to repeat.
 * Lipstick Lesbian: Lakshmi
 * Loan Shark: Averted by Sheldon, to the cast's and viewers' surprise. Apparently, loaned money is the only thing which Sheldon is not a neurotic, schedule-obsessed jerkass about, if only because the only money he lends is money he doesn't need for anything in particular.
 * Local Hangout: The Cheesecake Factory, largely by virtue that Penny can be involved with the scene while she is working. The Comic Book Shop also comes up in later seasons.
 * Logic Bomb: At least for Zach...

"Drunk Girl: You're such a good listener!"
 * Looking for Love In All the Wrong Places: Leonard, at the end of Season 3 and the better part of Season 4.
 * Loser Gets the Girl: Leonard at Penny's Halloween party (though he ends up being Above the Influence).
 * From the same episode, Raj hooks up with a (admittedly) drunk girl. Specifically because he's too afraid to say anything.

"If cats could sing... they'd hate it too."
 * Lovable Nerd: Leonard and Raj.
 * Ludicrous Precision
 * Man Child: Sheldon. He insists that someone take care of him the way his mother would when he's sick, locks himself in his bedroom where no one else is allowed when he's furious, curls up into a crying ball of sad on his bed when he's embarrassed, runs away from home when he's upset, can't sleep alone in the apartment after it's broken into, and can be bribed with a toy robot. Up to Eleven.
 * Or a Thomas the Tank Engine toy with "real smoke."
 * Explored in "The Rhinitis Revelation".
 * See also Parental Substitute
 * Manic Pixie Dream Girl: In it's own way, this is what Penny is to all of the guys and especially Leonard. The guys are generally happy in their own closed-off world of science, sci-fi and comics and Penny encourages them to expand their social horizons a little. In a reversal, Leonard (and Sheldon to a similar degree) have introduced Penny into a different world of higher thinking and education. In "The Ornithophobia Diffusion" Leonard and Penny argued over how they hated the things they do together (Leonard hated doing karaoke at 2AM or going on hikes, Penny hated watching a documentary on dams), only to later use those same things when talking to other people about their "hobbies" to make themselves seem more interesting.
 * Master of the Mixed Message: Before Leonard openly admitted his feelings to Penny (she was well aware of his crush beforehand) she had given him several mouth kisses, once when drunk and once as a "happy birthday" thing. But it also shows this trope depends largely on interpretation as Leonard went into a mental maze analyzing Penny's reaction to a brief relationship he had with Leslie. He wasn't certain if it was "Genuinely happy you're with someone" or "Too bad you're taken now" and (post breakup) "Genuinely sorry it didn't work out" or "Glad you're now available."
 * Meaningful Name:
 * The names Sheldon and Leonard are a Shout-Out to television writer Sheldon Leonard.
 * Penny.
 * Interestingly enough, her name implies brightness—i.e. "bright as a penny". This may be the creator's way of implying that she, as she has actually shown in many episodes, has more going on up there than many give her credit for.
 * What's her name? Penny. Where is she from? Nebraska. What's the capitol of Nebraska? Lincoln. Where's a common place to find Lincoln's picture? On a penny. We're through the looking glass, people.
 * And also, "Penny for your thoughts?"
 * Barry Kripke is a Shout-Out to Saul Aaron Kripke.
 * Leonard's middle name is Leakey; his parents named him for archeologist and paleoanthropologist Louis Leakey. It's not related to his history of bedwetting.
 * His last name, Hofstadter, is a Shout-Out to Nobel laureate Robert Hofstadter and his son Douglas Hofstadter of Godel Escher Bach fame.
 * Possibly also to Richard Hofstadter.
 * Also, the second syllable of his first name is...you guessed it. Leonard lampshades this in "The Adhesive Duck Deficiency".
 * Sheldon shares a last name with Nobel laureate Leon Cooper.
 * Leon Cooper is the namesake of the Cooper pair, which might also be a good name for a Sheldon/Leonard ship.
 * Rajesh Ramayan Koothrappali.
 * Howard Wolowitz is "named after a computer programmer known by the show's co-creator Bill Prady."
 * His last name also sounds like a combination of "wallow" and "wits." He wallows in his own wit, as it were—or he would, if Sheldon didn't constantly deflate him.
 * The head of the Entomology Department at the University is Professor Crawley, he mentioned he had the nickname of "Creepy Crawley" in school.
 * Mary and Shelly Cooper have to be a shout out to the writer of Frankenstein.
 * Meanwhile Scene: In "The Stairway Implimentation", a flashback from Leonard contains one about what Sheldon does when Leonard, Raj and Howard left. Then lampshaded by Penny who notes Leonard couldn't have known what Sheldon did.
 * Meganekko: Bernadette, Amy, and Leslie.
 * Meta Casting: Mayim Bialik, who plays Amy, actually has a PhD in Neuroscience (closely related to Amy's neurobiology). That makes her the only one in the cast who understands her dialogue.
 * Metaphorgotten: Sheldon, referring to Penny's singing.

"Priya: My brother. He’s got a big crush on Bernadette. Leonard: What?! You’re kidding. Priya: No. I found poems he wrote about her. Very disturbing. “Oh, Bernadette, please play my clarinet.”... And for years, everyone in my family was convinced that HE was the clarinet enthusiast."
 * Milestone Celebration: Celebrated the 100th episode in the fifth season with an appropriately big episode.
 * Minor Flaw, Major Breakup: Leslie breaks off her brief relationship with Leonard when she finds out that, in her ongoing debate with Sheldon over whether loop quantum or string theory is the superior model of spacetime, Leonard doesn't actually care, and would have let their hypothetical children "decide for themselves" which one they thought was correct.
 * Minor Injury Overreaction: Inverted, on a date with Penny at the gun range Leonard shot himself in the foot. It turned out that it merely grazed his foot but Leonard tried to play it off as being badass that he had a gunshot wound.
 * Mistaken for Gay:
 * Leonard and Sheldon often introduce themselves as "living together" and causing people to initially jump to the wrong conclusion, done before the opening credits of the pilot episode. Raj's parents, after hearing Sheldon say he lived with Leonard, replied that they were "like Haroon and Tanvir." Leonard then intervened and explained the actual situation, although later as Sheldon ran to get their special-edition DVD of Fiddler on the Roof he remarked to himself that "maybe we are like Haroon and Tanvir."
 * Sheldon also once went looking for an available male to distract Penny from an online gaming addiction. His technique was to approach a man in the cafeteria and ask if he was in a sexual relationship. Getting a no, he replied, "Would you like to be?" and walked away with the man's number scrawled on his hand - possibly the sole example of someone successfully picking up a stranger in the series.
 * Raj and Howard. In the third season, Leonard's mom encourages them to tell each other about their latent homosexual attraction, and tells Howard to stop talking about girls because it's upsetting to his "partner". Not to mention that Raj's parents say that Howard is the closest thing to a daughter-in-law that they have.
 * Leonard's mother calling Raj and Howard a homosexual couple is introduced in her first appearance on the show, the Season 2 episode "The Maternal Capacitance". Leonard loves the concept so much that he brings it up again in the above-mentioned third season episode, "The Maternal Congruence".
 * According to Raj's sister Priya his whole family thought he was gay

"Leslie: Hey guys. (to Sheldon) Dumbass."
 * Modesty Towel: Penny calls out for help because she slipped and fell in the shower. She's able to get the attention of one of the male characters, who she convinces to come in despite the fact she took a shower (and presumably is naked). He walks into the bathroom, and despite that she can't move because she broke her shoulder, she's lying on the bottom of the tub completely covered by a towel.
 * Moment Killer: Happens plenty of times between Leonard and Penny, and on occassion with Raj and Howard with their own prospective love interests.
 * Mood Dissonance: Crops up here and there when the humour gets cringe-worthy enough, but the episode "The Staircase Implementation" deserves get a special mention. Everybody except Sheldon looks absolutely horrified and the Studio Audience... keeps... on... laughing...
 * Mood Swinger: Part of the premise is that Penny is a very emotional girl who frequently baffles the guys with her illogical mood swings, shown in the pilot where she explains her life (from Nebraska, works at the Cheesecake Factory, etc) and then suddenly breaks down in tears (with Sheldon and Leonard looking at each other with a "Huh?" expression). At several instances she will storm into the apartment and yell at the guys for whatever recent mishap or screw-up, but she is also quick to forgive. Sheldon, being Sheldon, will sometimes associate it with "her time of the month."
 * Mood Whiplash: Season 5 featured a visit from Sheldon's mother, Mary Cooper. Mary preferred to sightsee while Sheldon wanted her to do "mom things" for him. At the end of the episode, Sheldon gets sick and
 * Another season 5 episode wraps up with  and while contemplating this,
 * Ms. Fanservice: Penny. Her regular attire in the first two seasons was low cut tank tops and short shorts. Although it has gradually become averted as about mid-way through the second season she started showing less skin until the early third season where she hardly wears anything like that anymore unless going out to a party or dancing (although no less attractive).
 * Mundane Made Awesome:
 * The sequence when Sheldon and Raj try to solve the physics calculation on Sheldon's board: A series of still shots of them staring at the board, from different angles, set to "The Eye of the Tiger." Played for laughs, of course. With an aspirin break in the middle, during which the music stops. It resumes when the staring does.
 * Pretty much every time the guys play video games together, you can expect them to be chewing the scenery into oblivion. "I possess the SWORD OF AZAROTH!"
 * Mundane Utility: Leslie, such as using a large laser to heat up a cup of noodles, or flash-freezing and smashing a banana to put over Cheerios.
 * In "The Infestation Hypothesis" the guys use an expensive piece of lab equipment as a panini press.
 * Must Have Caffeine: Penny definitely seems to be this in the mornings. Drinking coffee while driving in the early morning is just one of the things she does that irritates Sheldon, and in the episode "The Vartabedian Conundrum", she comes into the apartment half-awake, saying desperately, "Out of coffee; need coffee."
 * My Beloved Smother:
 * Howard's mother.
 * Leonard's mother is an inversion; she is pretty much a female Sheldon. At one point, Leonard confesses to Penny that he built a hugging machine when he was a kid to use on himself.
 * And his dad borrowed it often.
 * My Friends and Zoidberg:
 * Leslie's usual approach to greeting the four guys.

"Wolowitz (miffed): I have a masters' degree! Dr. Gablehauser: Who doesn't?"
 * When Sheldon's planning to move away, a section from his videotaped goodbye message to Leonard, Raj, Howard, and Penny: "The four of you are three of my closest friends, and one treasured acquaintance." The lowly "acquaintance" in question turns out to be.
 * The fact that Sheldon, Leonard and Raj are all doctors and Howard technically isn't is pointed out by several characters, including Dr. Gablehauser, who pointedly addresses him as "Mister Wolowitz" and Sheldon, of course, who has referred to him as "Not-A-Doctor Howard Wolowitz."

"Penny: That means... Sheldon, you're a doctor. Leonard's a doctor. Amy's a doctor. Raj is a doctor. Bernadette is a doctor. And... Howard, you know a lot of doctors!"
 * When Sheldon gets a girlfriend who's a doctor and Wolowitz gets a girlfriend who's becoming a doctor.

"Sheldon:  "
 * Sheldon actually sees himself as this to Wolowitz. He refers to Raj as Wolowitz's best friend, Leonard as his secondary friend and himself as his tertiary friend.
 * My God, What Have I Done?: Howard says this when he and Raj find the perfect match for Sheldon at the end of "The Lunar Excitation".
 * My Hovercraft Is Full of Eels: Sheldon's attempts to learn Mandarin.

"Sheldon: You should have been here for the Great Jenga Tantrum of 2008. Leonard: You bumped the table, and YOU KNOW IT!"
 * My Rule Fu Is Stronger Than Yours: After years of putting up with Sheldon's ridiculously elaborate roommate agreement, Leonard starts dating a lawyer, who knows how to exploit every loophole in the language of the contract.
 * Played even straighter, when later Sheldon draws up a new roommate agreement that "benefits" himself greatly, then forces Leonard to sign it or expose them to Priya's parents.
 * My Sister Is Off-Limits: Raj invokes this when his sister comes to visit.
 * Naked People Are Funny:
 * Neat Freak: Sheldon.
 * Nerd Nanny: Penny.
 * Nerds Are Sexy: Pretty much the whole point of the show. The guys don't get laid despite their geekiness; they get laid because of it. (Except for the asexual Sheldon, for whom sex is less exciting than video games.)
 * In fact, the tagline of the show's first season was "Smart is the new Sexy".
 * Nerds Are Virgins: Plays with. It's pointed out early on that everyone, even Raj (although Sheldon has no interest whatsoever), has had some intimate moments in the past. Their love life isn't exactly a feast though.
 * New Powers as the Plot Demands: Howard was never seen demonstrating his ability to communicate American Sign Language until Season 5's "The Wiggly Finger Catalyst," although several times (including the pilot) he likes to make himself out as being a linguist (including knowing Klingon). It Makes Sense in Context because Howard acts as an interpreter between Raj and Raj's deaf girlfriend Emily in the episode, and as an in-joke that even with a woman Raj actually can date comfortably, Howard still has to be there.
 * Nice Guy: Leonard Hofstadter. And there is Zack, one of Penny's exes. He is conspicuously thick but in refreshing contrast to the rest of Penny's exes doesn't seem to have a bad bone in his body.
 * Nice Job Breaking It, Hero: Penny had a bad break up with an unseen boyfriend at the end of season one, and Leonard decided to go be a comforting friend (though admits to Howard he isn't her gay friend). As he tried to make her feel better about the situation (the boyfriend posted intimate details with her on his blog) she took from it that she should give him another chance and thanks Leonard for getting her to see the big picture, which left him with the irony of fixing her relationship. In a double layering of the trope Penny's attempts to reconcile with the boyfriend fell apart (due to him already in bed with another girl) and briefly got angry at Leonard for his "advice," leading Raj to say, "Wow! You managed to screw-up the screw-up!"
 * No Ending: "The Twenty-One Second Excitation" almost has a Bolivian Army Ending. In the final scene before The Tag, How is this resolved? Did they get away? Did they get trampled? Did Sheldon wind up in the hospital, or jail, or the loony bin? The Tag just cuts back to Penny, Bernadette, and Amy Farrah in Penny’s apartment. The episode ends there, and the plot is never revisited.
 * Several other episodes don't really resolve the story and just continue on with the next episode. In the second season premiere Leonard accidently insulted Penny when discussing their relationship and the episode ended with her closing the door in his face. It was some 5 episodes later we even learn that they had an uneasy agreement to stay friends and ignore their attempts at a romantic relationship, but the exact details of which are never seen.
 * No Guy Wants an Amazon: S4 Ep05, "The Desperation Emanation", Bernadette sets Leonard up with her tough friend, Joy. Leonard ends up being miserable on their date due to her overbearing personality, including constant references to how strong she is and how much she's into fitness and martial arts (including 101 ways to rip a guy's nuts off). Though just to have some sort of companionship he still agreed to be her date to a wedding.
 * No Indoor Voice: Mrs. Wolowitz.
 * "WHO'S CAWLING AT THIS UNGAWDLY HOWAH?!"
 * No Man Should Have This Power: Parodied in "The Precious Fragmentation", where Leonard announces that he's mailed the prop One Ring back to Peter Jackson where it belongs.
 * No Sense of Humor: Subverted by Sheldon; he's got one, it's just... very Sheldon.
 * Noodle Incident:
 * Sheldon's childhood seems to be filled with these. Among the ones mentioned are Sheldon's dad fighting a bobcat over some liquorice, his parents arguing as his father trap shoots the family's commemorative plates off the roof, his mom's secret smoking habit, trying to build a nuclear reactor in his back yard, trying to frighten neighborhood bullies with a homemade Death Ray, being chased up a tree by a neighbor's chicken, getting beaten up by his Hot Amazon sister, and losing an uncle who died chasing a badger up a chimney. Assuming Sheldon really Can Not Tell a Lie, it's a miracle he didn't turn out even more neurotic.
 * Amy's 'firm cervix' and her 'tilted uterus' was supposed to be next.
 * Penny was quoting her dad on how much he likes Leonard by comparing him to her rather peculiar collection of old boyfriends "Why can't you go out with Leonard? Leonard never tipped a cow on himself."
 * No OSHA Compliance: In "The Engagement Reaction" there is a patient in the hospital being treated with radiation sickness. As it so happens the door doesn't have a latch and swings open freely, allowing Sheldon (who is desperate to avoid any sick people) to accidently walk in without seeing the quarantine sign.
 * Notable Commercial Campaigns: To promote the Season 4 move from Monday to Thursday nights, the gang is seen sitting around eating food when Sheldon announces that he invented a transporter to help them move from Monday to Thursday. Everyone 'beams out' of their chairs then 'beam back in' in the exact same positions. Leonard notes that it doesn't feel very different, while Howard complains that his food is now cold.
 * In 2011 American cable channel TBS bought the rights to air The Big Bang Theory and advertised it by showing a clip from Family Guy of Peter jumping into midair and getting frozen there. After he says "Call a Scientist!" we cut to a clip from Big Bang of Leonard answering the phone. Oddly enough, the footage of Peter came from an episode which only five minutes earlier had featured a Big Bang parody complete with stars Jim Parsons and Johnny Galecki voicing their characters.
 * Not Distracted by the Sexy: Invoked by Penny for laughs on two occasions - One time, when the guys are discussing possible improvements to her entertainment system she makes the offhand comment that she would take all her clothes off because it's hot, and another time she brings three of her girlfriends to their apartment and offers to have sex with them while they are playing Halo 3. They don't even hear her.
 * Not Helping Your Case: Amy and Sheldon accused Leonard of being a sore loser after he "lost" an attempt at Counterfactuals. The game is very hard to win (unless you think like Sheldon and Amy), but Leonard's response didn't exactly do him any good...

"Penny: So who is she? Leonard: She's a doctor. Penny: Nice. A doctor doctor, or a you kind of doctor?"
 * Not So Different: Amy ended up looking through Leonard's yearbook and based on the comments noticed how unpopular he must have been, only to reveal that no one even signed her yearbook except her mother. This actually ended up as an ice breaker between them, who didn't really talk much before then.
 * Penny calls out the guys for making fun of Zack for not knowing much science in "The Justice League Recombination" when they were always bullied.
 * There are also indications that Penny may be a bit of a nerd herself, the one episode dealing with videogame addiction being the most noteworthy.
 * Not That Kind of Doctor:
 * In reference to Leonard's new girlfriend, an actual medical doctor.

"Police Officer: I'm sorry but I can't help you, Mr. Cooper- Sheldon: Doctor Cooper. Police Officer (looks over at Leonard incredulously): ...Seriously? Leonard: Not the kind with access to drugs."
 * Also happens when Sheldon calls the police to help with his hacked World of Warcraft account, from "The Zarnecki Incursion":

"Leonard: Anyone here know how an internal combustion engine works? Raj, Howard and Sheldon: Of course! Leonard: Any know how to fix an internal combustion engine? Raj, Howard and Sheldon: Not a clue."
 * N-Word Privileges: Lampshaded. Raj claims that whenever he talks about India negatively, it's not racist.
 * Object Ceiling Cling: Howard's faulty space toilet malfunctions, and during their attempt to fix it, he launches a piece of meatloaf onto the apartment ceiling. It falls down some time later when Penny is there.
 * Odd Name Out: Given in-universe to one of his "clowder or glaring" of cats by Sheldon. While he named most of them after scientists in the Manhattan Project like Dr. Robert Oppenheimer, one was named Zazzles because, according to Sheldon, "he's just so zazzy".
 * Off-Screen Breakup: Howard and Bernadette. They got back together, though.
 * Official Couple: Leonard and Penny. It was semi-official as of the pilot episode, and they were an actual couple for most of season three.
 * Sheldon and Amy.
 * Oh Crap: Penny in "The Roommate Transmogrification" when she
 * Sheldon when he realizes that he
 * Omnidisciplinary Scientist: Sheldon, a string theorist who on his days off also dabbles in, for example, genetic engineering, and who purportedly built a nuclear reactor and a "death ray" as a child. This Depends On The Writer, though: we've also seen him unable to ascertain how to open a toolbox.
 * Truth in Television - anyone who's ever worked with extremely high-IQ academics will marvel at their often-paired lack of common sense and/or inability to perform mundane tasks.
 * This trope is generally subverted on other occasions, Howard (the engineer) boasts that he designs items for the international space station but he has no idea how to fix the elevator and when their car breaks down Leonard has this to ask:

"Sheldon: I'm afraid I can't allow that. Pursuant to Starfleet General Order 104, Section A, you are deemed unfit and I am relieving you of command. Leonard: Starfleet General Order 104, Section A does not apply in this situation. Sheldon: Give me one good reason why not. Leonard: Because THIS IS NOT STAR TREK!"
 * Once a Season: A couple of recurring gags you can expect every season: "Soft Kitty" being sung to or by Sheldon, Leonard and Sheldon's parents visit (although somewhat sporadically), everyone appears in costume for some event (Halloween party, Renaissance fair, the punishment for losing a game...) and from the third season on, at least one appearance by Wil Wheaton.
 * One Head Taller: Penny is generally about the same height as Leonard (whose short stature is frequently commented upon) but when she wears heels she suddenly towers over him.
 * One of the Kids: All of the characters to some degree (yes, even Penny), but Sheldon essentially acts like a self-centered child who needs to be mothered by Penny or whoever else is around, especially when he's sick. A scene that leaves a lasting impression is after she takes Sheldon to Disneyland (in one of the episodes centering around her UST with Leonard), and as he is asleep with his Mickey ears still on, Penny and Leonard watch him from the bedroom door like they were his parents.
 * In another episode, Sheldon runs away from home after Leonard and Penny get into a fight. The two manage to coax Sheldon into returning after promising not to fight anymore and Penny forces Leonard to buy him a toy. However, in this case, Sheldon was more than just the typical Man Child he usually is, he had literally become like an upset grade school aged child, possibly due to childhood regression due to his parents constantly fighting, for that time he actually once again became the young boy in Texas dealing with his mother and father fighting which they took Up to Eleven once again. Speaking of his mother, although he displays Man Child tendencies around his friends, he literally becomes an eight year old all over again when his mother is around.
 * On the other hand, Howard's overbearing Jewish Mother still treats him as if he's a child, which he loathes. Not that he always argues against it, or is even completely aware of it. Despite that, he has moments where he wants Bernadette to be a mother figure, such as when he asks her to drive him to the dentist and lets slip "mothers take their kids to the dentist all the time".
 * "Soft kitty, warm kitty..."
 * Only One Name: Penny's last name has never been revealed in the show. When Leonard and Penny decide to have a wedding (after eloping), none of her family have last names either.
 * Only Sane Man: Mostly Leonard. Since his fixation on/relationship with Penny drifted away from center stage, this has become a big part of his role.

"Penny: You know, in Star Trek when they go into battle they put their shields up... (realizes what she just said) ...Where the hell did THAT come from?"
 * Ordered Apology
 * Outdated Outfit: Leonard's collection of ugly suits, including a felt maroon-ish one. Sheldon also has a suit more appropriate for the 1930's.
 * Out-of-Character Moment: When a new, pretty girl moved upstairs and was manipulating the guys with her looks Penny had a conversation with her in the laundry room. She tried to explain the idea that they don't know how to put their shields up...


 * This fuels the comedy when Sheldon is the only one to help Penny when she dislocates her shoulder in the shower. Penny asked him to try to be "comforting" and Sheldon's attempt to be comforting is so alien that Penny is visibly disturbed by it.
 * Out-Gambitted: Sheldon tries the old "joy-buzzer" prank on Howard by getting Howard to shake Sheldon's hand with the buzzer attached. Howard collapses and Bernadette is immediately upset, reminding Sheldon that Howard has a heart condition. Bernadette pulls out an adrenaline needle and insists that Sheldon inject it into Howard's heart, claiming not to be strong enough to do so herself. Howard opens his eyes and reveals the ruse. This one seems like it had to have taken some planning and anticipation on Howard and Bernadette's part for whatever Sheldon had in store, but it may have been easier if you factor in Howard's familiarty with The Sheldon as demonstrated in the above Improbably Predictable example.
 * It gets even better when Sheldon smacks himself in the forehead for falling for it and gets a dose of his own joy-buzzer.
 * Overprotective Dad: This trope is intentionally invoked/subverted by Penny's father Wyatt, who really likes Leonard and considers him far above the dumb, brawny jocks she usually dates. When he discovers that they actually didn't get back together,.

P-T
"Penny: (reading a trivia game card) Tweety Bird will often say 'I tawt I taw a...' what. Sheldon: (after several seconds of tense, non-verbal communication with Leonard) ...Romulan?"
 * Freudian Trio: Discussed by the writers at a convention, Leonard occupies a space where he is pulled in two directions: a greater world of human social interaction with Penny and a seclusive world of math and science with Sheldon. It thereby makes Penny The McCoy, Sheldon The Spock and Leonard The Kirk.
 * Pac-Man Fever: Averted to some extent: They do use realistic sound effects for the games, show actual Age of Conan screens, and showed Howard and Leonard boxing in Wii Sports. However, they never actually show their Halo matches (likely due to copyright), and some of the commentary is a bit off (at one point, they mentioned a "health pack" in Halo 3 and charging a plasma rifle when a plasma pistol is the weapon that does that). In another episode, they show some gameplay footage from Mario Kart Wii, and even then, it's not shoehorned.
 * In one episode, Sheldon sits out in the hall playing Super Mario 64 on his laptop via Emulation as he can't use the console in the apartment. The sound effects are entirely correct. However, he also mentions the his mother sent the memory card along with the console. The N64 did have memory cards, but they were only compatible with certain games. Mario 64 was one that saved directly to the cartridge.
 * Also, in a zigg-zagging example of the trope, in the episode where Sheldon's apartment is "visited" by burglars, he lists all the consoles that have been stolen (A list consisting of an Xbox 360 and every Nintendo home-console from the NES to the Wii), and a list of games after that (such as The Legend of Zelda Twilight Princess and Call of Duty.).... Only problem is, he doesn't list any games for the Super Nintendo he supposedly had. He ends the list with "oh, and Ms. Pac-Man".
 * For what it's worth, Ms. Pac-Man was available on Super Nintendo.
 * Paintball Episode: The guys play on their own time and there is some company activities there with teams divided by department (apparently the pharmacology department were hyped up on experimental steroids). They are generally accurate to the game, using masks that reasonably cover the face and body armor, although they do remove their masks when in a bunker. As common for the trope, they are strategizing and constantly worrying about when their "time" will come.
 * Parental Substitute: Penny is often forced to mother Sheldon. This sometimes includes Leonard acting as a father, including Sheldon being frightened when they fight and after the break-up where they act like divorced parents. Sadly, this partially comes from Sheldon having bad memories of his parents fighting.
 * Passive-Aggressive Kombat: Sheldon
 * Perma-Shave
 * Personality Swap: A very mild version, but Penny once dislocated her shoulder and was taken to the hospital by Sheldon. Returning home high on painkillers, she convinced Sheldon to sing "Soft Kitty" to her. Usually the roles are reversed.
 * There are a few times where the other characters mimic Sheldon's idiosyncratic door knocking, specifically Penny when Sheldon stole her laundry during an Escalating War.
 * Picked Last: After Penny and Leonard break up, Sheldon is asked whether he's on "Team Penny" or "Team Leonard." He answers, "Whichever team picks last," since that's how it happened when he was in high school (unless there was a kid in a wheelchair).
 * Made all the funnier by the fact that Sheldon never went to high school to begin with.
 * Pity Sex: The proxy version. Leonard and Raj hire a prostitute for Howard on a trip to Las Vegas that happens right after Leslie Winkle breaks up with him, though any sex that might ensue is glossed over.
 * Penny blasted Howard for being a creepy sleaze, hurting his feelings. When she goes to apologize, he tries to kiss her, and has his nose broken. When the guys hassle him about it, he says "The way I see it, I'm halfway to pity sex".
 * Plato Is a Moron: Sheldon compares himself to Isaac Newton in one episode, declaring that "Gravity would have occurred to me without the apple."
 * Poor Communication Kills: After Leonard and Penny's first date, she confided in Sheldon that she lied to Leonard about getting a community college degree, and swore him to secrecy. Sheldon nearly went crazy holding it in, and told Leonard only when he was drugged up on Vicodin. Leonard assumed Penny was embarrassed over not completing college and tried to show support by giving her a Community College brochure. The problem was Penny didn't care so much about college as she was worried Leonard considered himself too smart for her, and him bringing over the brochure validated her concerns. This is largely the reason for their romantic false start in the second season.
 * Poor Predictable Spock: Aside from being the only thing anyone picks in Rock Paper Scissors Lizard Spock, Sheldon is always thinking of Spock when playing 20 Questions.
 * He also considers himself the Spock of their "away team". (Leonard is Kirk, Howard is Scotty, and Rajesh is "that guy who always gets killed.")
 * Pop Cultural Osmosis Failure: Goes in two ways, Penny failing to recognize the geeky stuff, and Sheldon & Co. not knowing relatively normal things.

"Leonard: They're on my tail! ...But it's prehensile so I can handle them."
 * Portmanteau Couple Name: In-universe. "Shamy" in the Season 4 Premiere for Sheldon and Amy.
 * Amy is quick to put an end to it, though.
 * Precision F-Strike: After Sheldon says that Howard's robotic hand is no more than a minor upgrade from fast food animatronics, Howard makes the hand give Sheldon the finger. Subverted since it ended up giving him the peace sign.
 * Sheldon rarely swears, so when he does it comes as a surprise. He swears more often when quoting someone than of his own accord: "He was very understanding; he said, 'Got you back jack, bitches be crazy'".
 * Amy invited Leonard to be her date to a wedding and made a conscious effort to be social and engaging, with Leonard not really being good company. Eventually she calls him out on his moping around and said, "I have a kinda-sorta boyfriend who is playing with model trains tonight and you don't hear me bitching about it."
 * Prehensile Tail: Parodied in an episode as the foursome are playing a group roleplaying game as bad guys approach.

"Leonard: We're at Code Milky-Green! Repeat! Milky-Green! Howard: Dear God! Not Milky-Green!"
 * Product Placement:
 * All of Chuck Lorre's recent projects, including Two and a Half Men, use and place Safeway products around the set.
 * All of the gang's shirts are available for purchase (most of them can be found here), as is the periodic table of elements shower curtain.
 * One that's more subtle, but Warner Brothers owns the show (alongside DC Comics) and the vast majority of comic references comes from DC, and the comic shop the guys frequent seems to only sell DC titles (and Madman.) But Marvel comics, as well as smaller companies and series, do show up from time-to-time. (Perhaps most notably the episode with guest star Stan Lee).
 * Episode 5x07 had several #1 issues from the September DC reboot. Presumably those issues will be missing the page adverts for this show.
 * After being synidcated to TBS, the station has two different forms of the trope going; A), using clips from the show and splicing in TBS (sometimes pretty badly), and B) having static shots of the main apartments, particularly the guys' formula boards, where the product placement of the day equals funny/delicious/good (anything from pizza to beer to a service) even if the show doesn't have anything to really do with the product.
 * Put on a Bus:
 * In "The Plimpton Stimulation", Bernadette. Offscreen, no less.
 * The Bus Came Back: She returned in "The Hot Troll Deviation" becoming a regular character
 * Leonard's doctor girlfriend in the second season. In her last appearance, Leonard was afraid she was getting too close, but the episode seemed to end with everything turning out all right. Then she was never seen or talked about again.
 * Leslie Winkle, which is lampshaded when Leonard goes to see her and she remarks its been around 18 months since they last spoke.
 * Queer People Are Funny: With a rare female example with Amy, who has an unhealthy obsession with Penny.
 * The Rainman: Sheldon, to some extent. Also either subverts or takes this trope to the extreme, depending on your point of view.
 * Some of the nastier aspects of him seem to have been based on the writings of J. Arturo Silva, a forensic psychiatrist who famously diagnosed Jeffrey Dahmer with Asperger's.
 * Random Number God: 5x04 Sheldon decides to let dice make his every pointless decision.
 * Ranked by IQ: Sheldon often uses his IQ as a 'proof' that he's correct.
 * Real Life Writes the Plot: Penny was absent for two episodes in Season 4 and was behind the bar of the Cheesecake Factory when she returned. This was to work around Kaley Cuoco suffering a compound fracture in her leg after she fell off her horse and it stepped on her leg.
 * Real Song Theme Tune: Barenaked Ladies' "The History of Everything".
 * Really Gets Around:
 * Leslie Winkle is implied to be this, referring to waking up on a futon with half a dozen strangers as a reason to try and settle down with Leonard.
 * Penny objects to being perceived this way after Sheldon calculates the number of men she's slept with in her lifetime based on her current statistics. The thing with Penny isn't that she sleeps around but that she really appreciates a physical relationship with her boyfriends, she just seems to have a new boyfriend every other week in the early seasons.
 * Rearrange the Song: As Theory entered 5 night a week syndication in 2011, Barenaked Ladies' wrote and preformed a number of different versions of the lyrics to the Real Song Theme Tune "The History of Everything" mentioning the cast by name, which aired in short ads shown after the first commercial break.
 * "The Reason You Suck" Speech: Penny's brutal rundown of why Howard is a lonely creep instead of the suave ladies' man he fancies himself to be.
 * Reckless Gun Usage: An interesting case is that Penny is shown using proper procedure in clearing the chamber before loading the clip with the safety on. Doesn't stop Leonard from shooting himself in the foot.
 * Red Alert: Sheldon getting a cold is serious enough to cause Leonard to run out of the apartment in the early hours of the morning, frantically calling everyone so they can bunker down and avoid looking after him.

"Sheldon: I made a boo-boo in front of Stephen Hawking! *faints* Stephen Hawking: Great... another fainter!"
 * Reed Richards Is Useless: All of the scientists on the show are fairly accomplished, but to keep the premise from overwhelming the average episode they are unlikely to make any major contributions to science and engineering. As well Sheldon is not going to prove string theory or otherwise get a Nobel Prize because however smart the science consultant may be, they are unlikely to have a Nobel Prize worthy theory in their back pocket.
 * When Stephen Hawking points out that Sheldon made an error in his mathematics, meaning that his revolutionary theory about the Higgs-Boson is actually completely wrong.

"Mrs Cooper: He thinks he's such a smarty-pants, he's no different from any man. You tell 'em not to do something, that's all they want to do. If I hadn't told my brother Stumpy not to clean out the wood-chipper by hand we'd still be calling him Edward. Now, don't you move - I'll bring over all the food. Leonard: No, I can do it."
 * Relationship Upgrade: Between Leonard and Penny, at the beginning of season three..
 * And, as of 5x10,.
 * Religious Robot: Discussed. When the boys talk about having their consciousnesses implanted into robots, Howard says that his robot would have to stay Jewish because "I promised my mother." The others talk about how Howard would have to power down on Saturdays and have his rabbi discuss with the manufacturer about getting circumcised.
 * Remember the New Guy?: Raj's sister, Priya is introduced in Season four with a full back story explained in exposition, plus a never-before-mentioned.
 * Retconning the Wiki: At one point, Raj admits to vandalizing Wikipedia.
 * Reverse Psychology: Sheldon's mother uses this to get Sheldon and Amy back together when they break up in "The Zazzy Substitution".

"Professor Crawley: Let me ask you a question. What does an accomplished entomologist with a doctorate and twenty years of experience do when the university cuts all his funding? Raj: Ask rhetorical questions that make people feel uncomfortable?"
 * Rhetorical Question Blunder:

"Leonard: I'm just glad Sheldon didn't rat me out to the landlord... or the police... or Homeland Security..."
 * Roaring Rampage of Revenge: A literal one in "The Good Guy Fluctuation" by Sheldon, victim of a Halloween prank from Leonard. Early in the episode, Sheldon insists that Leonard open a mailbox, only for Leonard to find junk mail. When Sheldon goes to open the mailbox, an airbag with Leonard's face pops out, scaring Sheldon. Sheldon gets Leonard back by hiding in the apartment couch while Leonard is sitting on it talking to Priya. When Leonard is done, Sheldon pops out of the couch roaring, wearing a green shirt, purplish zombie makeup and fake blood on his lip. Sheldon: "Bazinga punk! Now we're even!"
 * Robosexual: Raj gets a little too attached to his iPhone.
 * Howard has a bit of trouble with the robot arm he built in the season four opener.
 * Rock-Paper-Scissors Lizard Spock. Poor Predictable Spock.
 * Romantic False Lead: Some for Penny, some for Leonard—although his are more Little False Leads, in that he'd always prefer to be with Penny.
 * Rooting for the Empire: Some in-universe examples.
 * In the second Christmas ep, Leonard said that Sheldon roots for the sun when watching Frosty the Snowman.
 * He also likes the Grinch until the Grinch has his change of heart.
 * In the third episode of the fourth season Sheldon explicitly stated a preference for the Empire when Leonard used the Rebel Alliance as an analogy for their group.
 * Rule of Funny:
 * The episode where Sheldon's World of Warcraft account got hacked - while the desperate lengths the foursome get into to try recovering his items (including going into a Black Market in Goldshire, of all places, and Raj volunteering to seduce someone for the information), but completely ignores what actually happens when a WoW account gets hacked, and the reasons for doing so.
 * And the episode where Howard's background investigation for security clearance was conducted by an FBI agent instead of someone from the Office of Personnel Management.
 * And then another episode's scene where Raj had bought a very nice area rug at Big Lots, but ended up with eleven extra rugs because it was only available in a case of twelve. In reality, Big Lots only sells single rugs, and they're not available (in store) by the case.
 * Rule of Three: Sheldon knocking on a door, any door.
 * Lampshaded when Penny opens the door after two, and then supplies the third herself.
 * To which he responded, "That's just wrong."
 * When Sheldon saves Leonard from.

"Sheldon: No spaces."
 * Sheldon has a bad breakfast: orange juice - "In what universe is that non-pulp?", English muffin - "In what universe is that 'lightly toasted'?" and margarine - "Well, I have no difficulty believing you're not butter."
 * Rules Lawyer: Played straight with Sheldon, who exploits the Roommate Agreement for all it's worth. Then hilariously inverted when Leonard gets his own literal Rules Lawyer who then proceeds to exploit every technicality in the Agreement for all it's worth.
 * Running Gag: Some for each character
 * Sheldon:
 * His idiosyncratic door knocking, three sets of three knocks, with the name of the person on the other side between each knock. And when he does it to Penny, her responses to such. Notable examples of this are when Penny turns it into a door knocking war (repeating his knocking pattern from the other side of the door and saying his name) and when Sheldon knocks as The Flash.
 * "I'm not crazy! My mother had me tested." and "Bazinga" (a coined term Sheldon made to identify when he is pranking someone.
 * "Coitus", originating with Howard in the pilot but often used by Sheldon as a substitution for the word "sex."
 * First confirming that what someone else said was a joke before giving a slight titter in response.
 * "That's my spot."
 * Soft Kitty is sung at least once a season and almost always interrupted; whoever's singing it always has to start from the top, not where they left off.
 * Leonard:
 * Lactose Intolerance and other dietary restrictions.
 * The Face Palm, befitting his Straight Man character
 * Penny:
 * Her general ignorance of most geeky pop culture, including Stan Lee and having never watched Raiders of the Lost Ark. This has been played down in later years because of her close proximity to the guys she has come to learn much of that stuff.
 * Penny's "check engine" light is constantly on, Sheldon and others bug her about attending to it, and she refuses.
 * Penny's use of the guys' wifi, and Sheldon changing the password to something like pennygetyourownwifi.

"Penny: And what kind of doctor removes shoes from asses? Sheldon: Depending on the depth, that's either a proctologist or a general surgeon. Leonard: *holds up sarcasm sign*"
 * Raj:
 * His knowledge and familiarity with more "girly" topics such as loving Bridget Jones Diary and knowledge of fashion.
 * Raj is a magnet for Slumdog Millionaire jokes.
 * Not being able to talk to or around women without being drunk or influenced by other substances.
 * Howard:
 * His lack of a Ph.D
 * Being Jewish and doing his best to follow Jewish rules while still being his lecherous self.
 * Actually, he only cares about Jewish traditions during the high holidays. This is a guy who had Sheldon buy him a bacon cheeseburger. What he wants is to appear to follow the rules for his mother's sake, although she doesn't seem to have a problem with Bernadette, a Gentile, being engaged to her son.
 * His top-volume screaming matches with his mother.
 * Bernadette:
 * Her proximity to experiments involving dangerous bacteria like yellow fever and combining Ebola with the common cold.
 * Her inability to understand a joke (though it disappeared after a few episodes).
 * Her height (Melissa Rauch is actually just under 5').
 * Sounding just like Howard's mom when yelling or upset.
 * Amy:
 * Childhood pranks being pulled on her.
 * Her infatuation with Penny, both as simply best friends and with some homosexual undertones.
 * Using her harp to play songs that normally are not played on the harp (like TV theme songs or Bon Jovi)
 * Sarcasm Blind: Sheldon does understand sarcasm... meaning he knows what the word "sarcasm" means and is able to use it himself. He's just bad at detecting it.

"Sheldon: *knock knock knock [*Penny from behind the door* Who do we love!] Penny.
 * Say My Name: WHEATON!!!!! Also a Shout Out to The Khan.
 * Used by Penny once when Sheldon came knocking.
 * knock knock knock [Who do we love!] Penny.
 * knock knock knock [Who do we love!] Penny. [Penny finally opens the door]"

"Raj: I am talking to you?! *Shakes hand* Hello Penny! How are you?!"
 * Second Episode Introduction: A variation. While Raj met Penny in the pilot, it took him until getting drunk in the eighth episode before he could actually talk to her and properly introduce himself;

"Sheldon: "Roommates agree that Friday nights shall be reserved for watching Joss Whedon's brilliant new series, Firefly." Leonard: "Does that really need to be in the agreement?" Sheldon: "Well we might as well settle it now, it's gonna be on for years.""
 * Seductive Spy: Joyce Kim, as portrayed in "The Staircase Implementation".
 * Self-Induced Allergic Reaction: Howard eats a nut bar to stall Leonard so they could set up Leonard's surprise birthday party. And because Penny was going to hook him up with her easy girlfriends.
 * This is after he fakes an allergic reaction to the same thing for the same cause, only to realize the group wouldn't have enough time. And well...
 * Self-Insert Fic: Sheldon has written a Star Trek fan fiction as a child, in which the crew recognize his abilities as a Child Prodigy and take him aboard.
 * Serious Business: Amongst many other things (of which the weekly routine of meals and evening activities are just a small part), in the episode "The Hofstadter Isotope" a discussion about who would succeed Batman in the event of his death between Sheldon and an online community eventually leads to Penny's date being cut short after he is brought into the discussion as well.
 * World of Warcraft to Sheldon. When his account gets hacked he calls the FBI... and when they hang up on him he calls the regular police.
 * Sesquipedalian Loquaciousness: Sheldon talks like this a lot. Even to Penny.
 * All the episode titles.
 * Sexy Shirt Switch: Penny in the third episode of the third season, after her and Leonard's first night in his apartment and she was dancing and making French toast.
 * She Is Not My Girlfriend:
 * Leonard and Penny in an early episode.
 * Sheldon toward Amy throughout Season 4.
 * She Who Must Not Be Seen: Howard's mother, Mrs. Wolowitz, who is also The Voice.
 * Ship Sinking: Amy is pretty much this to the popular Penny/Sheldon ship. In particular, "The Flaming Spittoon Acquisition" not only shows how serious Sheldon is about Amy, but even dedicates a scene to addressing why he is not compatible with Penny.
 * Sheldon's speech even uses some of the most common elements for the ship that appear in just about every "Shenny" fanfic, which Penny then proceeds to tear down one by one. The ship isn't only just sunk, it never existed.
 * Ship Tease: Played with between Leonard and Amy. Amy coerced Leonard to be her date for a co-workers wedding (Sheldon doesn't like going because there weren't any other scientists his age) and Amy ended up cheering Leonard out of a funk. To his own surprised he enjoyed spending time with her and gave her a kiss on the cheek for a goodbye, with Amy misinterpreting it as being that Leonard had fallen for her. Of course, the kiss on the cheek was part of the commercials for the episode.
 * Again in Season 5 when Sheldon asks Penny on a date to make Amy jealous when she begins to date Stewart.
 * Shipper on Deck:
 * Most of the main cast ships Shamy (Sheldon/Amy).
 * And at least Leonard's mother ships Howard/Raj.
 * As of "The Boyfriend Complexity",
 * Sheldon ships Leonard/Stephanie very strongly in "The White Asparagus Triangulation".
 * Shot to the Heart: Sheldon tries to prank Howard with an Electric Joy Buzzer, but Howard appears to collapse from a heart attack and is instructed to stab a syringe of adrenaline straight through his heart. Of course, it all turns out to be a counter-prank.
 * Shout-Out/Reference Overdosed: When the four come back from their Arctic expedition, Leonard, Howard, and Raj all have grown caveman-like hair and beards, while Sheldon has a perfectly-groomed goatee... just like the one alternate-universe Spock had.
 * Sheldon's various superhero T-shirts.
 * Sheldon named their bowling team "The Wesley Crushers" meaning that they would crush Wil Wheaton. Everyone else (including Wheaton) saw it as a Fan Shout Out to the actor.
 * In the episode guest starring Stan Lee, the judge who  is named "J. Kirby".
 * In "The Friendship Algorithium", Sheldon says Howard drew a big-balled raccoon on the test Sheldon gave him. Turns out it may have been a reference to the anime film Pom Poko.
 * In the fourth season New Year's episode, the gang (plus Penny's current boyfriend, Zach) dressed up as members of the Justice League of America for a party at the comic book store. Others were dressed as the Fourth Doctor, a Hogwarts student, and The Joker, among others.
 * Just one more subtle: "The Apology Insufficiency" featured guest star Eliza Dushku. Towards the end of the episodes Sheldon tries to get Howard to forgive him for a mistake by "reprogramming" him.
 * Sheldon's line "Of all the overrated physicists in all the labs in all the world, why does it have to be Leslie Winkle?"
 * There are several shout outs to Battlestar Galactica. They range from the characters talking about watching the show to Leonard, as Howard puts it, "taking out his aggressions on innocent Cylons" (i.e. he destroys a Cylon action figure with a laser).
 * Don't forget Cylon Toast! Everyone loves Cylon Toast.
 * Many shout outs to Star Trek both old school and new school. Penny gives Star Trek figurines to the guys, Sheldon is at first upset that he missed the Star Trek reboot then upset that he didn't get a Leonard Nimoy Spock standee, a quick Lt M'ress mention, Sheldon's feud with Wil Weaton, Sheldon compares their friends to a landing party ("Now we have a Dr. McCoy!"), and of course...."Do you know what this means? I possess the DNA of Leonard Nimoy!!!"
 * There was an ironic shout-out to Firefly by Joss Whedon in "The Staircase Implementation":

"Sheldon: Sheldon’s journal. Security system in place. However, sleep continues to elude me. I’ve seen the underbelly of Pasadena, this so-called City of Roses, and it haunts me. Ah, the injustice, I lie here awake, tormented, while out there evil lurks, probably playing Donkey Kong on my classic Nintendo."
 * Sheldon's journal in "The Bozeman Reaction" is a shout-out to Rorschach's Journal in Watchmen.

"Penny: What's a "multiverse"? Sheldon: [turns to Leonard] "Get her out of here.""
 * Strangely enough, there is no mention in that episode that Bozeman, Montana where Sheldon decides to move to was also the location in Star Trek: First Contact where humanity made first contact with the Vulcans. You'd think Sheldon of all people, would have brought that up.
 * Shown Their Work: The show goes well out of its way to get the details of the science and tech stuff right, as well as generally listing actual things that geeks are into like Halo and Battlestar Galactica. Not only that, they have an actual physicist, Dr. David Salzberg, on hand to fill in the correct dialogue and write appropriate diagrams and formulas on the white boards. All of this leads to Genius Bonus. This includes:
 * Sheldon's search for magnetic monopoles in the second season finale was based on actual research being done at the time, with results posted over the season break. Similarly, his dilemma figuring out the contradiction with particles moving through a graphene sheet was related to contemporary research that later won the Nobel Prize.
 * Rivalries between different scientific specialties is also on the nose, with the show focusing much of it with Sheldon (Theoretical Physics) vs Leonard (Experimental Physics), Raj (Astrophysics) and especially Howard (Engineering, no Ph.D). Sheldon also holds a particular disdain for Geologists.
 * Comparatively recent events in geekdom including a conversation involving the meaning of Final Crisis, shake-ups in the Batman comics run and the re-establishment of the DC Comics Multiverse.

"WHEEEAAAATOOOOOOONNN!!"
 * In "The Thespian Catalyst" Penny tries to teach Sheldon about acting and eventually gets to Improv. Sheldon kept going off on tangents (asking for frozen yogurt at a shoe store) and Penny was rolling with it, which only confused Sheldon because (obviously) there is no such thing as a shoe warehouse/frozen yogurt hybrid store. Penny then explained the number one rule of improv, you say "Yes" and accept all scenarios given.
 * "Shut Up" Kiss: Leonard has a habit of rambling on topics irrelevant to what he is trying to get at (going on about how Indian food helps clean out your colon when inviting Penny to lunch in the Pilot). As him and Penny grow closer romantically Leonard will still ramble on and Penny will quiet him down with a kiss, like so.
 * Sibling Yin-Yang: Sheldon's fraternal twin sister, Missy.
 * Sibling Yin-Yang: In "The Luminous Fish Effect", after talking about what a pain Sheldon is, Sheldon's mother tells Howard that God didn't give her more than she could handle; she has two others kids who are "dumb as soup."
 * More specifically, while Sheldon is a theoretical physicist, his twin sister Missy is a hostess at Fuddruckers.
 * Significant Reference Date: In the episode entitled "The Excelsior Acquisition", Sheldon finds a traffic summons conserning an traffic incident that occured on 11/16, the airdate of "The Adhesive Duck Deficiency" in which the violation happenend.
 * A Simple Plan: Played with in "The Loobenfeld Decay."
 * Single-Target Sexuality: Amy's early insistence that she has no interest in romantic love or physical contact ("up to and including coitus") takes on difference shades when she very openly admires Penny's "secondary sexual characteristics" and even suggests "harmless lesbian experimentation" at a sleepover. That said, she never shows any interest in any woman other than Penny.
 * Sitcom Arch Nemesis: Barry Kripke, Wil Wheaton and Leslie Winkle at different points, all for Sheldon.
 * Skyward Scream: Also a Shout-Out to Wrath of Khan.

"Sheldon: [to Raj] How could you think my favorite amino acid was glutamine?"
 * And as typical for this show, it's a perfect recreation of "KHAN!" and not the osmosis version. Sheldon doesn't actually look up at the sky, he looks straight ahead with a close-up and screams "WHEATON!" and then the camera cuts to an Astronomic Zoom pulling away from Earth.
 * Sleep Cute: Howard and Raj.
 * Sleeps with Everyone but You: Poor Leonard, pining after Penny while listening to her complaints about sleeping with her jerkass boyfriends on every extreme way.
 * Slow-Loading Internet Image: A video variation. Leonard and Priya are communicating through teleconferencing and are attempting to have a long-distance intimate date. Leonard takes off his clothes, but when Priya starts to take off hers, the signal freezes just as she's taking off her bra.
 * Small Name, Big Ego: Sheldon and his intelligence, one of the show's myths.
 * Small Reference Pools: Usually very good at averting this, although it sometimes sacrifices realistic characterization for (comparatively) more familiar references, like the time Sheldon said Ubuntu was his favorite Linux distribution.
 * Notably, no self-respecting nerd would be caught dead playing Monopoly when there are so many wonderful obscure German games about trading.
 * And of course, there was the questionnaire that Sheldon made for Raj, Howard and Leonard:

"Penny: Okay, well, what do you communicate about? Sheldon:"
 * Smart People Know Latin: Howard and Sheldon try to use this against each other.
 * Smug Snake: Sheldon and his sister.
 * The Smurfette Principle: Penny, so very much. Averted in later seasons with the addition of Bernadette, Amy, and Priya.
 * Snark Knight:
 * Penny took her role as the Nerd Nanny a bit more seriously in earlier episodes and berated the guys for their awkward, sometimes inconsiderate tendencies. This lead to a few instances of Not So Above It All and, eventually, One of Us. She can still be pretty brutal, but talks to them on their own terms.
 * Prime example in "The Cooper-Hofstadter Polarization" where Sheldon tries to make Leonard's head explode a la Scanners. Later, Penny finds a picture of herself on Wolowitz's website (listing her as his girlfriend) and does it to him.
 * Southern-Fried Genius: Averted with Sheldon, who very rarely speaks in his native East Texas drawl.
 * Spiritual Successor: To 1941's Ball of Fire.
 * Spit Take

"Sheldon: *after being outvoted* I never get my way. Leonard: *dumbfounded* You always get your way! Sheldon: *beat, thinks about it* Regardless..."
 * Spock Speak: Sheldon.
 * Spoiled Brat: Sheldon.

"Leonard: What happened to your new friends? Sheldon: I had to leave. They were having fun wrong."
 * Stalker with a Crush: Ramona in "The Cooper-Nowitzki Theorem", who is more in love with Sheldon's mind than him.
 * Standardized Sitcom Housing: On the whole the show uses the typical set-up, with the hallway between apartments used extensively for scenes and conversations. But there are moments where they get camera angles showing the "fourth wall" with a completed set, one being a POV of Sheldon coming in from the hallway when the others were staging an intervention on his refusal to get a driver's license.
 * The show manages a fairly clever recycling of the set by using the center hallway to represent three different floors with a minor redress, allowing a Walk and Talk with only one set.
 * Status Quo Is God: Lampshaded by Sheldon. After  he suggests they treat their relationship like a malfunctioning computer and restore it to the last point they both agree that it worked (which, given that this is Sheldon we're talking about, is quite a mature thing to suggest).
 * Stealth Pun: Cylon toast. Even better: that's a real toaster.
 * Stoners Are Funny: Leonard, Raj, and Howard in "The Adhesive Duck Deficiency".
 * "Stop Having Fun!" Guys: Sheldon's approach to any hobby he might happen to share with other people.

"Penny: This is how it feels when I say something stupid to you, isn't it?"
 * Stop Helping Me!: In the second episode Leonard and Sheldon got a spare key to Penny's apartment, which Sheldon used to clean her apartment in the middle of the night (with Leonard begrudgingly helping), leaving a note confessing to the act and offering advice on further organization. When she understandably freaks out, Leonard demands Sheldon apologize, to which he tells Penny, "I would like to apologize for what happened and I take full responsibility... and I hope this doesn't color your perception of Leonard... who I hear is a gentle and thorough lover."
 * Stupid Sexy Flanders: Penny's ex-boyfriend Zac has this effect on Amy Farrah-Fowler. It's played with because she's usually Asexual.
 * Early season one Penny started dating a guy for the first time and Leonard was a little miffed about it. When the others pressed him they asked "Is it because he looks better than you?" and Leonard admitted that it was true, "He was rather dreamy."
 * Stylistic Suck: Sheldon and Amy's podcast "Fun with Flags".
 * Super OCD: Sheldon is powered by this.
 * Surrounded by Idiots: Despite being surrounded by geniuses, Penny has common sense that none of the others possess.
 * This forms a lot of Sheldon's frustrations towards Penny, which gets reversed in "The Shiny Trinket Manuever" where Sheldon keeps getting distracted at a jewelry store;

"Bernadette: "So we are just going to sit here and wait for something to happen?" Howard: "I did that with you when we watched The Notebook...""
 * Survival Mantra: Here's Sheldon's.
 * Take That: Quite a few, largely to non-geeky movies.

"Raj: I'm the new homo in town... that came out wrong."
 * "The Flaming Spittoon Acquisition" tabs at card battle games with the guys being initially disgusted with "Mystic Warlords of Ka'a's" latest expansion adding Wild West characters to a fantasy-themed world, but find themselves unable to resist buying and playing it.
 * Thanks for the Mammary: Sheldon, to Penny. He didn't bump into her, though; he was helping her get dressed when she dislocated her shoulder in the bathtub—with his eyes closed.
 * Although he later admits that he was lying when he said he hadn't looked.
 * Amy was constantly wanting more physical contact with Sheldon, even coercing him to snuggle one night. Later Sheldon and Leonard went to pick her up from a liquor store parking lot Leonard was the one to help her to her feet and walk to the car and she happily exclaimed "Looks like someone finally found 'Second Base!'"
 * That Came Out Wrong: In "The Roommate Transmogrification" when Raj proves himself to be a better roommate than Leonard, Sheldon compares Leonard to Homo Erectus saying that he, like Homo Erectus, has been replaced by something better. Raj then makes a comment he regrets.

"Howard: Oh, no... that's not a good name."
 * Sheldon would often make awkward analogies and Double Entendres and not recognize what he was saying as sounding weird or odd, with everyone else having to explain why. When the group offered to help Sheldon overcome his stage fright they suggested he could considered them his X-Men. Sheldon appreciated the sentiment but suggested that since the X-Men were named after Charles Xavier, his team should be named after Sheldon Cooper and be called the C-Men.

"Penny: *laughs* I just asked Sheldon to get me into bed!"
 * Penny when she's doped up on painkillers and she asks Sheldon to help her get into bed.

"Penny: Of course this makes me uncomfortable, can't you tell? Sheldon: I really have no idea, I don't really excell at reading facial expression and body lang... Penny: I'M UNCOMFORTABLE SHELDON! Sheldon: ...thank you that's very helpful."
 * That Makes Me Feel Angry: Sheldon is not good at reading people's emotions at all, so about the only way to tell they are upset or uncomfortable at all is for them to tell him outright.

"Sheldon: Look on the bright side. Leonard: What bright side? Sheldon: It's only nine more months until Comic-Con. Leonard: [smiling] Oh yeah!"
 * Theme Tune Cameo: Subverted. Howard's ringtone is the theme tune, but the one from the unaired pilot.
 * There Are No Girls on the Internet: Sort of. When Penny walks into a comic book shop, all the guys - and there are only guys - stop and stare. A far more egregious example: a Running Gag to the effect that, while female scientists exist, few if any are "doable", so they don't really count as women. Of course, the latter was said by Howard.
 * Also inverted as that was the only reason Amy Farrah Fowler was found as match to Sheldon.
 * Think Happy Thoughts:

"Raj: Don't worry, nothing happened between me and Howard! *Beat* Not with 200lbs of Sailor Moon between us!"
 * This Is Going to Be Huge: In the flashback episode at the end of Season 3. While making out the roommate agreement, Leonard asks if Friday night being Firefly night needs to be in the agreement. Sheldon responds that they might as well decide now, because the show is going to be on for years.
 * This Loser Is You: At least if you're a Nerd. Or if you're not a nerd.
 * Those Two Guys: Howard and Raj, and their "ersatz homosexual marriage". Although they aren't as directly connected to Sheldon, Leonard and Penny (by virtue of not being neighbors or roommates), they do manage to do activities seperate from each other and the others but do play up the Ho Yay undertones in certain episodes.
 * A Threesome Is Manly: Raj drunkenly reveals during Howard's bachelor they once had a threesome with a overweight woman dressed as Sailor Moon;

"Howard: All right, this is an exact duplicate of the Wolowitz zero-gravity human waste disposal system as deployed on the international space station. Raj: Don't you mean the Wolowitz zero-gravity human waste distribution system?"
 * Time Travel Tense Trouble: Season 8 episode 5 has something like this, although the characters in this show seem to get it a lot better than the vast majority of characters in other examples.
 * Toilet Humour: Toilet Humour IN SPACE to be specific, and done rather well for once in "The Classified Materials Turbulence", where the gang has to fix a malfunctioning zero-gravity toilet. To quote Sheldon: "Apparently there is no law of diminishing comedic returns with space poop".

"Leslie: How can we have a relationship if we don't believe the same thing? How are we going to raise the children? Leonard: I guess we'll wait until they're old enough and let them decide what theory they would like for themselves. Leslie: You can't let them decide, Leonard; THEY'RE CHILDREN!"
 * Sheldon had some flatulence problems after eating brussels sprouts in an episode where he becomes hyper health-conscious.
 * Sheldon insists on anyone spending the night to have a specific time to use the bathroom (which doesn't interfere with his time), and is proud to say that he is "as regular as a German train schedule."
 * There are many jokes referencing Leonard's lactose intolerance too, which makes him flatulent; although, this is never shown on-screen.
 * Toilet Seat Divorce: During Leonard's brief "official" relationship with Leslie, she broke up with him over the fact he had a preference towards String Theory (which Sheldon brought up) while she is on the Loop Quantum Gravity. To the average viewer this is ridiculous, but to these super-geniuses it is Serious Business.
 * Also played as Does This Remind You of Anything?:

"Sheldon: Did you get the chicken shredded? Leonard: Yup. Sheldon: Even though the menu says it's cubed, not shredded? Leonard: Yup. Sheldon: Did you get the low-sodium soy sauce? Leonard: Yup. Sheldon: Did you get the good spicy mustard? Leonard: Yup. Sheldon: Excellent. (beat) What took you so long?"
 * Too Much Information: Usually involving Amy Farrah Fowler.
 * Took a Level in Badass: For a certain qualification of "badass." Leonard started off the series being painfully shy and uncertain of himself, it took him the entirety of the first season to officially ask Penny out. It's implied that interacting with Penny has helped boost his sense of self-worth and he progressed from being a nice, generic guy to becoming one of the more scathing Deadpan Snarkers and having a relatively successful love life (even outside of Penny). By season five he had several moments where he demonstrated a personal backbone, though he still needs work on when and where to choose his battles.
 * In parallel Character Development, we've also seen Penny Take A Level In Nerd. (The first one is wonderfully illustrated with a Double Take at herself, while the studio audience applauds.) In addition to random science-fiction analogies, she has quite a bit more patience and higher standards when it comes to dating.
 * Trademark Favorite Food: Whenever the five main characters are eating together, it's Chinese food. Although it's not so much trademarked for Sheldon as it is ISO 9000 specified.


 * But when it's just the four nerds together, they seem to have (slightly) greater variety in their diet. They go to various restaurants, including the Cheesecake Factory where Penny is a waitress. Also, at work they have generic cafeteria food together in some cafeteria presumably on the Caltech campus.
 * It completely covers Sheldon though. He has a strict menu that he eats per day, for all three meals, and presumably snacks as well. The Chinese food has to be from Szechuan Palace. (Unfortunately for Sheldon, they closed two years ago. Now his cashew chicken comes from Golden Dragon.) He's similarly disappointed see that they've gotten Indian food from Mumbai Palace, not their usual Tandoori Palace. When Penny makes french toast for breakfast, he complains that it's "oatmeal day". When Leonard and Penny leave, he comments that the food does smell good, then finishes with "too bad it's not french toast day" and dumps the rest into the trash. He also seems quite fond of milk and tends to drink it more often than might be expected, especially if the other diners have wine or champagne.
 * Inverted with Raj, who has expressed his distaste of Indian food many times.
 * And then there was the time Sheldon was alone for the night and ordered Kadai Paneer. Consider: He can only order it when the others are away, because of Raj's distaste for Indian food, Howard's peanut allergy, and Leonard's lactose intolerance. His meals are usually very regimented, but in this instance he was willing to break the pattern to order it. No wonder he called it "a symbol of my independence."
 * It's also very sweet, in its way, since the Sheldon we know and love usually does not hesitate to force his own preferences on other people.
 * Training Montage: Parodied when Sheldon and Raj intently study a whiteboard... complete with fast cuts and "Eye of the Tiger" playing in the background. Twice.
 * Truth-Telling Session: On "The Irish Pub Formulation", Leonard's confession of snowballs into one of these.
 * TV Genius: Parodied in one episode, where Sheldon and Raj have a Hard Work Montage to Eye of the Tiger. It's literally just them staring at a whiteboard of equations.

U-Z
"Leonard: It's actually one of the few idiosyncrasies of his, that doesn't make you want to kill him."
 * Uncle Pennybags: Sheldon of all people. When Penny falls behind on her rent and her car breaks down, he freely gives her enough money to pay for both of them. Despite her assuminption that Sheldon's obsessive tendencies would lead him to hound her, it turns out that he's incredibly lax when it comes to lending his money. He honestly doesn't care when its paid back, as long as it eventually is.
 * Lampshaded by Leonard as one of his saving graces;

""We're here to see Koothrappali, not kill Batman!""
 * Uncomfortable Elevator Moment: The elevator's been broken for literally the entire series, so instead, awkwardness occurs while climbing the stairs. Penny and Raj's sister Priya share one of these (intentionally drawn out to make the audience uncomfortable) in Season 4.
 * Understatement: After he worked up the nerve to ask her out in the first season finale, Penny admitted to Sheldon that she knew Leonard had "a little crush" on her. Sheldon responded with "A little crush. I suppose so, like how Menelaus had "a little crush" on Helen of Troy."
 * Undisclosed Funds: Raj's parents are apparently "Richie Rich"-rich, according to Sheldon. When asked how much that is, he just says that it's somewhere between "Bruce Wayne"-rich and "Scrooge McDuck"-rich.
 * Unlimited Wardrobe: Partially averted. While the characters have a very extensive wardrobe, they do repeat outfits from time to time, mostly the guys.
 * Unrequited Love Switcheroo: Leonard/Penny/Priya
 * The Un-Smile:
 * Sheldon provides the current page image in the episode "The Griffin Equivalency":

"Penny: "I call everyone sweetie." Sheldon: "You tramp.""
 * Unusual Euphemism: "Frickity Frack, not this again!"
 * Unwanted Gift Plot: Amy gives Penny a bad painting of the two of them in "The Rothman Disintegration".
 * Valley Girl: Penny falls into this from time to time, even though she's originally from Nebraska.
 * Vanity Plate: The Chuck Lorre Production notes which give you a split second to read a long paragraph. Even the short ones with a picture and a caption usually takes a Freeze-Frame Bonus to appreciate.
 * Verbal Tic: Penny likes to call people "Sweetie." In a bout of confusion Sheldon used it as evidence that she has feelings for him.

"Sheldon: Why on Earth are you telling me all this ? Leonard: I don't know... Sometimes your movements are so lifelike I forget you're not a real boy."
 * Vocal Dissonance: Bernadette normally has a fairly high pitched, squeaky voice. But there are times when she yells and sounds exactly like Howards mom. Which he finds to be hot.
 * Howard being the stereotypical television Jewish man will never be rid of his mother, in any form.
 * Vocal Evolution: Melissa Rauch's voice for Bernadette was always pitched higher than her own natural voice, but her first few episodes it was still fairly natural sounding. Later episodes it is quite higher, almost to Helium Speech. Funny enough, when Bernadette gets angry her voice lowers in pitch.
 * Carol Ann Susi as the voice of Mrs. Wolowitz has always had No Indoor Voice, but was slightly more muted and with less enunciation in her earlier "appearances."
 * The Voice: Howard's mother, Mrs. Wolowitz, She Who Must Not Be Seen.
 * The Voiceless: Rajesh, whenever he's with a woman—unless he's drunk.
 * Voice for The Voiceless: Howard, who usually just relays what Raj whispers into his ear (though sometimes Howard's annoyed comebacks imply what Raj said well enough).
 * Volleying Insults: Sheldon hates Leslie Winkle for being the only woman able to be actually more deliberately unpleasant and insulting to him than he could be to anybody else. Cue their constant rows when both meet.
 * Wacky Marriage Proposal: Howard pulls this on Bernadette when she asks where their relationship is going.
 * His subsequent retraction of the proposal for an Anguished Declaration of Love is both cringeworthy and utterly hilarious. Subverted in that Bernadette sees it as the most romantic thing anyone has ever done for her.
 * Walk and Talk: Lampshaded by Sheldon:

"Sheldon(knocking on the door): "All my friends." "All my friends." "All my friends." Howard: I think its like Beetlejuice...we mentioned his name too many times!"
 * The central hallway set is redecorated to represent three floors that the characters consistently have to climb (usually Once an Episode). They use it for a Walk and Talk in addition to a couple of Uncomfortable Elevator Moments.
 * We Want Our Jerk Back: In a variation Sheldon balked at switching up his regimented dinner plans and refused to go to Raj's place with everyone else. The rest of the group spent the Sheldon-free evening talking about how annoying he could be, only to realize the group felt empty without him around.

"Leonard: Oh geez. Does this suit really look that bad? Sheldon: Forget your suit, look at my arms waving. I'm like a flamingo on Ritalin."
 * What Do You Mean It's Not Heinous?: In-universe and Played for Laughs. When Leonard is invited to see the Large Hadron Collider in Switzerland on Valentine's Day and insists on making it a romantic holiday with Penny, instead of taking Sheldon as was agreed to in the Roommate Agreement, Sheldon is very angry and plays a driving game with him called "Traitors" where he names three historical traitors and Leonard is to put them in the order of the magnitude of their treachery. First round: Benedict Arnold, Judas, and Dr. Leonard Hofstadter. When Leonard protests against being included in the same category as these men, Sheldon even hints that Judas ranks somewhere below Leonard.
 * When talking about the horrible things that would happen at his birthday parties, Sheldon confessed to Penny with great anguish that he got a motorized dirtbike instead of a titanium centrifuge. Sheldon simply could not understand what child would like such a gift, and was genuinely perplexed when Penny said that most kids would love it.
 * What Happened to the Mouse?: Season 2 has a three-episode arc where Leonard dates a medical doctor, Stephanie, who sort of stealth-moves into his apartment. He spends that whole third episode trying to find a way to get her to move back out, but being diverted because she keeps jumping his bones. She isn't explicitly stated to have broken up with him (when he finally does spit it out, her response is to, well, jump his bones)... and by the next episode Leonard appears to be single again, with no mention of Stephanie.
 * This was also played with in an episode where Penny decides to stay in Leonard and Sheldon's apartment for the night. Raj walks out of the shot right before she walks into the room and asks to stay. Leonard, Penny, and Sheldon all have the whole argument about her staying there and then, once that's all over and it's decided that Penny stays, they turn out the lights and all go to bed. Cut to Raj, who was in the middle of eating a sandwich in the kitchen. He quietly leaves the room, looking like he has no idea what just happened.
 * In "The Psychic Vortex" Raj and Sheldon managed to acquire dates with two very hot, intelligent and slightly geeky girls (one of whom played by Danica McKeller) named Abby and Martha, and even got a second date shortly after. What made these girls really unique was that the ice-breaker was Sheldon carrying Green Lantern's power battery at a party and they fully knew what it was; they ended up playing Rock Band back at Sheldon's apartment. Not to mention that Sheldon even appeared to enjoy talking with Martha (discussing Flatland among other things) with Raj and Abby making out on the chair. It can be assumed that Sheldon's Asexual nature really disappointed Martha, and that took Abby away from Raj. But these were girls who could relate to them in interests, intelligence and were attracted to them because of it (not even Penny can really claim that with Leonard), with no follow up episode it almost seems to be a waste.
 * In "The Ornithophobia Diffusion" the episode ends with Sheldon about to "become a mommy" to a baby blue jay, after the parent bird had left behind their nest. What on Earth became of the poor bird?  Is Sheldon still waiting for the egg to hatch?  Is he in fact a mommy, but doing all his parenting duties off-screen?
 * What the Hell Is That Accent?: When Barry Kripke is first introduced with his strange speech impediment (reminiscent of Elmer Fudd), Raj asks "What part of America is that accent from?", but his question is summarily ignored.
 * Who's on First?: Done in "The Alien Parasite Hypothesis" with Amy telling Sheldon about her reaction to Penny's ex, Zack. "Hoo."
 * Will They or Won't They?: For the first two seasons, Leonard and Penny.
 * Wimp Fight: Leonard and Sheldon get into a fight at a seminar in the first season, which is largely a push, shove and slap fight. They are subsequently shown on YouTube and are clearly embarassed over how silly they look:

"Leonard: "Wait, if you guys never talked, what did you... Never mind. Stupid question.""
 * The wrestling match between Howard and Raj also counts, which consisted of over a half-hour of circling each other on the mat. Leonard fell asleep waiting for something resembling a fight to happen.
 * Also the time Sheldon and Barry played one-on-one basketball for a vacant office. (They chose sports so that they would have a level playing field, since it's the one thing they're both equally bad at.) They go forty-five minutes without sinking a single basket.
 * With Friends Like These...: It's not entirely clear on why Leonard, Howard and Raj are friends with Sheldon and vice-versa. The three have little tolerance for his personality quirks, see him as a source of irritation, make fun of him behind his back, and are often mocking and unsympathetic when he's humilated. Sheldon meanwhile shows them no respect, ridicules Leonard and Howard's work, and is so stubborn, selfish and demanding that the gang agrees with whatever he wants to do because it's easier than arguing with him.
 * Penny once questioned why the other guys stay friends with Jerkass Sheldon. The answer: "We like Leonard." Sheldon managed to save Leonard's life and kept Leonard out of prison, so he's indebted to Sheldon, but Howard and Raj fall back to "We like Leonard".
 * Women Are Wiser: Played with. Usually Penny or another female character is the one with the most common sense of the group, but sometime Leonard or others, including Sheldon are the ones to point out things the others never seen.
 * Women Prefer Strong Men: All of Penny's ex-boyfriends are muscular and dumb.
 * Written-In Infirmity: Averted. When Kaley Cuoco (Penny) fractured her leg at the beginning of season 4, Penny was absent for two episodes and no reference was made to her not being around. Once she returned the writers decided that her character would have a new bartending assignment at the Cheesecake Factory and be shot from the waist up behind the bar. A Vanity Plate was dedicated to new rules to ensure the safety of cast members, including any extreme activities (Kaley was injured while riding horses).
 * Xanatos Gambit: Arguably done in "The Good Guy Fluctuation" when Howard and Raj reveal themselves as the pranksters behind the attempt to scare Sheldon at the office. But to paraphrase Homer Simpson, their zany scheme was a front for an even zanier scheme. Anticipating that their relatively tame and cliche hijinks wouldn't scare Sheldon, Howard and Raj seemingly admit defeat in Sheldon's office when a man wearing a mask of the alien from the end credits of Star Trek: The Original Series pops out behind Sheldon's white board, successfully scaring Sheldon. The man unmasks;
 * It's a Xanatos Gambit in that they forsaw that their intial pranks would fail but a Kansas City Shuffle in that the initial pranks were a distraction from the true scaring attempt.
 * You Answered Your Own Question: When Penny tells Leonard that everything goes wrong with their relationship when they talk, she adds that she had an 8 month long relation with a guy named T.J. and they never talked.

"Sheldon: "Strawberry Quik!!! My favorite pink beverage! Just beating out Pepto-Bismo!"
 * You Never Did That for Me: Penny mentions Leonard haven't let her talk him into cooler dressing/hobbies as much as he let Priya.
 * Your Favorite: For Sheldon - Strawberry Quik

"Raj: Alright, not your mother. How about... your grandmother. Sheldon: No! I call no Mee-maws!"
 * When Amy decides it's time their relationship moved ahead (much to Sheldon's protests), she decides to get him to associate all his favorite things with her. In addition to the above strawberry Quik and spaghetti with little hot dogs cut up in it, she played the Super Mario Bros. theme song and played doctor Star Trek style, uniform and all.
 * Your Mom: Invoked by Raj in order to try to get Howard to let go of "The One Ring". Then Sheldon gleefully notes that if they turn on each other, he will get The Ring by default, Raj and Howard to decide to team up against him. Sheldon lists his mother's faults before they get a chance to, leaving them to bring out the big guns.


 * Howard's mother is a living Your Mom. It's implied that every single thing said about Mrs. Wolowitz is actually true, but since she's never visible on-screen, the audience simply must Take Their Word For It per Rule of Funny.