Remember, you can't spell "fangirl" without F-A-N-G.
The defining characteristic of a Fangirl (at least when the term is being applied negatively, which this description assumes) is that her love for a particular thing is obsessive yet shallow. She will be able to go on and on about how awesome her favorite female character is or how sexy her favorite male character is and will be willing to talk endlessly about what pairings she ships and why, but any attempts to have a meaningful, intelligent discussion with her about her supposedly beloved topic will be met with a glassy, uncomprehending stare and any criticism (no matter how mild or constructive) will be met with anger and sometimes even violence. Likewise, if the author does something with her favorite character that she doesn't like (even if it makes perfect sense within the universe and continuity, fits the characters previously established personality and tendencies, is well explained and justified, makes for a good meaningful story, or even if it's the only possible, logical outcome given the circumstances within the story), the Fangirl will usually react by turning on the formerly beloved author. Usually the Fangirl only approves of plot developments that favor her favorite character. Similarly, a Fangirl will tend to stay with a fandom or series no matter how much its quality deteriorates (through any amount of Flanderization, Adaptation Decay, etc.) and will even cheer for changes that negatively affect the quality of the story as long as they lead to her favorite character receiving preferential treatment or being featured more prominently. The Fangirl doesn't care about good story telling, she only cares about seeing more of her favorite character (whom she usually only likes for aesthetic reasons) and having her personal fantasies regarding said character validated in universe.
Simply a girl who is obsessed with something or someone, capable of Squee to Earth-shattering levels. Fanboys do exist but they're usually scary in an entirely different way. The stereotypical fangirl is, well, a girl who loves a fictional canon exclusively for one or more of the male characters, usually distilled down to a couple personality elements and/or appearance to the exception of other things such as backstory, abilities, and Character Development within the canon itself. Often, this obsession is a sexual fetish. Fangirls have existed for longer than you may think: the David Duchovny Estrogen Brigade was a terrifying force on The X-Files' group on USENET (a sort of Bronze Age webforum).
When her interests gravitates around the Boys Love and Yaoi Guys, we are in front of a Yaoi Fangirl, the scariest type for a certain side of the public... that being the side that's met them. Expect declarations within the target fandom of It's Popular, Now It Sucks when girls start liking it and "polluting" the forums with their "simplistic" view of the canon, spawning Flame Wars between these two groups because it's Serious Business on who is considered a true fan of the subject in question. Fangirls will be accused of Completely Missing the Point due to their frequent disregard for anything outside of a couple characters and their relationships.
Real-world fangirls of all types are leading causes of Draco in Leather Pants, Misaimed Fandom, Ship-to-Ship Combat, Crack Pairing and Crack Fic, and the addition (or removal) of trying to clarify things. If they're a Periphery Demographic, they may insist they are actually the primary (or, failing that, that they're the ones that "get it"). Besides the leather pantsing, they are often fond of Fanon featuring Motive Decay, Flanderization, Badass Decay, Woobiefication, Die for Our Ship, and... well, the list goes on. Conventional wisdom, realistic or not, is that Most Fanfic Writers Are Girls.
It is not always a pejorative term (though this being the internet, it often is); some people use the term "fangirl" to mean nothing more than a female Nerd—that is, a fanboy's legitimate female counterpart. A woman or girl describing herself as a fangirl is not necessarily a cause for alarm.
- Rena of Higurashi no Naku Koro ni goes nuts over anything she thinks is cute, announcing her intention to take said object of her affection home. In the second season, the perpetually-stoned Takano reveals her terrifying fangirl side over the dark legends of Oyashiro-sama.
- Demashita! Powerpuff Girls Z: Momoko (Blossom) has a triple dose of this:
- Mendou in Urusei Yatsura had a formal organization of fangirls following his every move, and ready to punish Ataru for any perceived infraction against him.
- Gary's Cheerleaders.
- Halca Hepburn from Legendz, untill she grows out of it.
- Renge in Ouran High School Host Club is a very educated Fan Girl. Of course she spends more time criticizing and advising the members of the Club than fangirling them, but when she fangirls she does it big.
- Minto from Tokyo Mew Mew is a closet fangirl of Tall, Dark and Bishoujo model and actress Fujiwara Zakuro. Remove the "closet" (pun not intended, but strangely appropriate) after Zakuro joins the team.
- Subaru of Magical Girl Lyrical Nanoha StrikerS is the titular character's personal fangirl. Half of her spells are named after Nanoha's and in the supplementary manga chapters set before the third season, she carries around a magazine clipping of Nanoha on her person at all times. It may have something to do with the small fact that Nanoha saved her life when she was 11...
- Motomiya Jun of Digimon Adventure 02 is a living embodiment of this trope, going so far as to chase down the cool, aloof, and completely uninterested Ishida Yamato whenever within sight. Once it becomes clear that he's interested in Sora, she moves onto Jou's older brother. An audio drama seems to imply that they eventually have some kind of relationship: she visits him on Valentine's Day and gets introduced to his parents.
- Naruto has Sakura and Ino who spent the first half of the series fangirling Sasuke Uchiha. Thankfully they got better and stopped. But in the second half of the series, which takes place after a Time Skip, we are introduced to Karin and Shiho, who both (especially the latter) alternate between calm and level-headed scientist-types to squealing fangirls for Sasuke and Shikamaru.
- An, Tomoka and Sakuno from Prince of Tennis, each girl in her different ways.
- In Sailor Moon, Minako turns out to be a fangirl of an idol singer - an important plot point in the end.
- Also happens with the Starlights; particularly Ami, which shocks everyone.
- Ohno, Ogiue, and Ohno's friends Angela and Sue from Genshiken, though they're more realistic than most portrayals of fangirls (aside from Ohno and Angela's exaggerated proportions).
- In her earliest appearances, Misato-chan seems to exist solely to fangirl Nana and the Black Stones, to the point of ignoring school, moving in with them to act as a fetch-and-carry girl, and even using a fake name to stump Yasu's attempted background check.
- Konata Izumi from Lucky Star is a rare example of a different type of fangirl. She is not interested in shipping or attractive male fictional characters. She has some of the characteristics of a typical male Otaku, watching tons of anime, addicted to video games, and likes to cosplay. Some of this may be influenced by her father, who is also an otaku.
- Emily Sevensheep of Mahou Sensei Negima is a massive Nagi fangirl. In fact, many females in the Magic World are Nagi fangirls. There's a reason why being amongst the first 100 to join the official Nagi fanclub is considered a special thing. Hell, being in the first five digits is considered a big deal.
- Her classmate Beatrix is a Rakan fangirl.
- Ayaka runs the line between being a Negi fangirl and being a Shotacon. Most of the class think it's the second.
- Kallen is Zero's biggest fangirl throughout most of Code Geass, complete with a Bodyguard Crush when Lelouch sees the true value of her devotion and puts her in charge of his personal defense.
- Kaguya's an even bigger example.
- Yumi from Mariasama ga Miteru gathers quite an extensive group of fan girls in the course of the series. She is the undisputable center of attention during the tea party she and Yoshino organize to find a suitable soer—much to Yoshino's chagrin.
- Kanade from Candy Boy has her own personal fan girl in Sakuya. She doesn't seem too happy about most of the time, but she also doesn't really try to get rid of her, turning poor Sakuya into a Hopeless Suitor.
- In Gundam Seed Destiny, Meer Campbell was so much of a fangirl for Lacus Clyne, she willingly became her Body Double and adopted her personality and, to a degree, her role.
- Tomoyo is Sakura's fangirl in Cardcaptor Sakura, in addition to loving her in other ways. Her obsession with filming all of Sakura's exploits even disturbs Sakura on occasion, and in an early episode, she gives an impromptu manifesto on Sakura's varied awesomeness to a boy who had just complimented Sakura on her athletic skill.
- Mei Chan fangirls after Ed briefly in Fullmetal Alchemist, until she finally meets him and sees the shortness of him. She then BSODs briefly before bawling him out for 'toying with her heart', and then moves her affections to Al, who is suitably tall. No pun intended.
- "Pipi" (the unnamed female character) from Saiyuki is a hard-core Kougaiji fan.
- In Kamichama Karin, Kazune and Michiru ("Micchi") have competing fanclubs, the Kazune-Z and Michirians. They argued over who should play the good prince and bad prince in the School Play, before the Kazune-Z eventually decided that an evil Kazune would be "sinfully delicious". Jin also has many, some of whom get downright violent.
- Nozomi of Chance Pop Session is a major Reika fangirl. The reason she joins the Akiba music school in the first place is for the chance to meet Reika. Even after having success as part of R-3, she still keeps her fangirl status.
- In Project A-ko, C-ko has been A-ko's fangirl ever since A-ko rescued her from the wolf that was about to attack her.
- Surprisingly, Yuki Nagato in the spin-off Melancholy of Haruhi-chan comes the closest ever to showing any emotion (thus far) by becoming the fangirl of an unnamed anime/game series.
- There's a couple of loony fangirls played for laughs in Darker than Black. This is due to the fact that the protagonist is a weapons-grade Chick Magnet; the fangirl in the OVA was also smart enough to recognize that the cute guy was the one who had saved her the other day (even if her logic was a bit... unique), leading to outright Stalker with a Crush behavior.
- Excel of Excel Saga is willing to take a bullet for her leader, Il Palazzo. Several bullets, in fact. And an antitank rocket. All fired by him.
- Misa in Death Note is a Kira fangirl in her first appearence.
- In Seikimatsu Occult Gakuin, Kozue loves everything supernatural.
- Tomoe Amamiya of Tiger and Bunny, Kotetsu's classmate back in high school, was a giant Superhero fangirl. Naturally, she ended up marrying one.
- In "Kuroshitsuji", Grell personifies many of the fans' emotions towards a certain demonic butler...
- Arrogant rich boy Mendou Shuutarou from Urusei Yatsura has a literal legion of fangirls after he transfers to Tomobiki High and all the girls there fall for him.
- Consummate geek Jason Fox loved the first two Lord of the Rings movies. Return of the King was less enjoyable; the difference being that his teen sister Paige was now an Orlando Bloom fangirl.
Paige: I hope Orlando is in every shot of this movie! Please, please, please, let Orlando be in every shot! You read Return of the King, Jason -- does Tolkien mention Orlando Bloom a lot? Wait, don't tell me! I want to be surprised!
Jason: (turns to someone off-panel) You, with the orc arrows -- please shoot me.
- A blog post eventually reveals that this is based on Bill Amend's wife's real-life fangirlism.
- Harley Quinn in all her appearances in Batman.
- Molly Hayes of Runaways used to be a major X-Men fangirl particularly when it came to Wolverine. Although once he showed up with Iron Man and Captain America (who had previously sent her to a foster home she ran away from) to arrest her friend Cloak, she decided he was a lot less cool in person.
- A minor villainess named Virtuoso that appeared in the Secret Six series is a huge Fangirl of the deceased Fiddler and is the current holder of his violin. When Fiddler appeared in front of her as a Black Lantern, he could see that she was brimming with love. She claimed to be his biggest fan, gushed about his past work, and even offered to return his original violin.
- The Official Fanfiction University of Middle-Earth has lots of them as students. They're brought there to get over it.
- The West Wing's Josh Lyman has in-show fangirls ("The Lyman Hos" and those from lemonlyman.com). A bit of Truth in Television, as he's pretty much Rahm Emanuel.
- Although it is also a little bit of Aaron Sorkin's experiences with commenting on Television Without Pity.
- Supernatural added an in-show fangirl Becky Rosen, who meets Sam and Dean in the first episode of season 5 and in the 9th episode of season 5, is a crazed fangirl who epitomizes the fangirl role as she can't seem to contain her excitement or stop touching Sam. And in one episode she even gave him a love potion, married him while he had it in him, took his pants, tied him to a bed, and almost went as far to sell her soul for more of the drug.
- And writing creepy Wincest fanfiction.
- In Castle, Detective Kate Beckett is a devoted fan of the novels of Richard Castle, and has been since before she met him. Since after meeting him he has exasperated and infuriated her in equal measure by tagging along on her investigations, she would rather die than have him find out. As such, she's something of an aversion in that she manages to restrain any squeeing urges she might have remarkably well; this is primarily to avoid giving Castle the satisfaction, however, and they have been in danger of slipping out on occasion.
- The webshow within a show of iCarly has an obsessed and annoying fangirl named Mandy.
- In Leverage, after Eliot plays the guitar once in public he gains a shocking amount of fangirls - in one scene they recognize him on the street and chase after him en masse. Later in the episode, Hardison spreads a rumor online, causing the fangirls to attack a car that they believe Eliot is in.
- In the show Power Rangers Ninja Storm, specifically the episode I Love Lothor, Lothor stars in a tv show ala I Love Lucy, which sways the minds of anyone who watches the show to fall in fangirl love with him through subliminal signals, instantly creating an army of fangirls who swarm the studio with homemade signs and attack anyone who dares say anything against Lothor.
- In Pretty Guardian Sailor Moon, Usagi and most of her friends are fangirls of Aino Minako, an Idol Singer who also turns out to be Sailor Venus.
- The Legend of Zelda: Twilight Princess has, once you win a specific mini-game, three squeeing fangirls who will follow Link as if he were a rockstar no matter where in the city he goes.
- Osu! Tatakae! Ouendan 2 has a scenario where the player cheers on a group of three middle-aged Fangirls trying to save their kidnapped idol.
- Betrayal at Krondor has the resident stoic badass Gorath run into a "an admirer" who's immediately all over him, causing him to do what anyone would do - flee.
- It's hard to tell if the fangirls in the Final Fantasy VII prequel Crisis Core are a show of affection or not. They obsess over the four First Class SOLDIERs in the game - making fanclubs, sending e-mails about insipid details, and even arguing amongst themselves - just as their real life counter-parts do. There is even a side-quest that involves helping them which directly influences the final number of members in Zack's own fanclub.
- Morgan LeFlay, Mighty Bounty Hunter(TM), from Tales of Monkey Island, is a rabid (and the only) Guybrush Threepwood, Mighty Pirate(TM), fangirl.
- In The Last Story after a sidequest you'll get a few of them, with a fanclub...
- Amy Rose from Sonic the Hedgehog.
- Good to finally meet you Commander Shepard. Kasumi Goto. I'm a fan.
- Since the above quote is not quite enough to show Kasumi's fangirlishness, she will keep shipping you with other teammates (especially Tali) and discuss your date with Kelly (though not for very long, due to the way her "dialogue" is written).
- Conrad Verner is a male example.
- In Solatorobo, if Red becomes a prize fighter, he'll get a fangirl named Toffee who almost confesses love to him before finding out that he's not the independent badass she thought he was. She later gets over it and starts crushing on him again - but by this point, she's made a name for herself and the move upsets her fanboys.
- Suikoden II has two fangirls, Cecile and Alanis, of Chris Lightfellow. Both want to be just like her, and Cecile is well on her way, but Alanis's talents lie in other areas.
- In Misfile fandom opinion is divided whether Missi is simply an over eager fangirl about Ash or a creepy Stalker with a Crush. It's strongly recommended to not mention the subject on the fan forum.
- A truly terrifying example exists in And Shine Heaven Now. Around once a year the Hellsing characters get glomped by numerous chibi-fangirls who Squee as they fly though the air and rant about how cool a character is after latching on. Even worse than this though is that the fangirls can also force people to act out their ships. In a recent storyline, the Major (a fanboy of War himself) turns this to his advantage. He gives a version of his 'I Love War' speech chock full of fandom terms to subdue the fangirls.
- There was also the Something*Positive storyline in which most of the attendees of a comic book convention were mauled to death (in variously creative ways) by a small army of angry fangirls.
- Kanaya is this towards Rose in Homestuck, having read her walkthrough. Suffered a mild case of Warts and All after actually chatting, but is apparently getting over it very quickly now.
- Also WV, after leading the Prospitians and Dersites to battle, he has many admirers, most of them female pawns from both sides.
- On Scratched Earth, Jane is Betty Crocker's No. 1 Fangirl and heiress to the company. Oddly enough, her Beta counterpart, Nanna, hated and feared the baroness, while her adoptive brother inherited the company.
- In Impure Blood, Mac, toward Roan. Though she does realize it could be unpleasant for him, she doesn't realize he might dislike "The Abomination".
- In Nip and Tuck, denying the impact on your life is weakened when a fan girl goes squee over you.
- Fontes' Rants: A recurring character is an unnamed fangirl who appeared in the very first strip obsessing over Inuyasha.
- In Sinfest, Monique meets her first fangirl, just when she has decided to rebel against the patriarchy. Her fangirl still worships her as It-Girl.
- Every time the young, handsome police officer Derek appears in the web fiction serial Dimension Heroes, it results in the two female leads going crazy.
- Dr. Horrible's Sing-Along Blog has two Fangirls and a Camp Gay Fan Boy. They worship (and stalk) Captain Hammer, and even engage in some Die for Our Ship against his faux Love Interest. After Hammer's humiliating defeat, they switch to Dr. Horrible, presumably because Evil Is Sexy.
- Despite the fact that Fangirls make up a major part of the site, Gaia Online felt the need to mock fangirls in their lost Rejected Olympics Manga. The main event? Escape The Fan, in which a rabid fangirl is released from a box to chase down a Friendly Neighborhood Vampire and an attractive (and female) Dark Elf. Gratuitous Japanese and hilarity ensues, culminating with the fangirl getting a nosebleed during an attempted (same sex) Kiss of the Vampire, and crying about her OTP when said kiss is interrupted.
- In the Whateley Universe, high school girl Fey has her own fan club chock full of fangirls who are also superpowered mutants. Not only does this mortify her, but her friends tease her about it.
- Official Fanfiction Universities deal with... curing ...fangirls. Sample students include:
- The Nostalgia Critic fits the stereotype more than he does the male version. When he likes something, he'll glee over it and go into Squee levels of excitement. More often than not he'll get crushed by the film making a bad move but it's still cute to see.
- While The Nostalgia Chick refuses to count herself as this, BFF Nella squees over most things.
- And Elisa is a huge fan of The Phantom of the Opera, writing Fanfic and having lots of merchandise!
- Iphigenie in Greek Ninja is a big one. She fawns over any guy that is officially hot (and even unofficially hot.)
- Sierra from season three of Total Drama Island is, as the series puts it, an "Uber-fan", she mentions that she's created fansites for each and every character and knows their eatings habits, hopes and fears and even their dental records. Needless to say, she creeps everyone out.
- In Avatar: The Last Airbender, a random posse of fangirls shows up in the Beach Episode when Zuko flings his shirt away. This is probably a shoutout to Zuko's massive Estrogen Brigade.
- In "The Warriors of Kyoshi" Kyoshi Island's girls mob Aang, to his delight, and Katara's annoyance. This was later Lampshaded by Azula in "Appa's Lost Days."
- Melody Juniper to Bart in The Simpsons episode, "Flaming Moe".