I Was Beaten by a Girl

Mal: What in the hell happened back there?
Wash: Start with the part where Jayne gets knocked out by a 90-pound girl 'cause... I don't think that's ever getting old.

—Serenity

Misguided masculinity says that a man cannot be beaten by a woman. Of course, any such man who is beaten by a woman is pretty unhappy.

Rationale for No Guy Wants an Amazon. Waif Fu may be in evidence. Related to Samus Is a Girl, if the man wasn't aware his opponent was female before losing.

Not to be confused with Abuse Is Okay When It Is Female On Male, but may be the reason some victims of that trope are afraid to come forward.

Examples of I Was Beaten by a Girl include:

Anime and Manga

Averted in Dragonball Z when Vegeta is thoroughly defeated by Android 18 - Vegeta was more concerned with the fact that he could be beaten at all despite finally becoming a Super Saiyan. He was actually angrier that it was a "machine" that did it than a girl.
One episode of Lucky Star happens in an arcade, where Konata beats several people in succession. When her opponents try to see who it is that beat them and realize it's a very young-looking girl, they quickly leave.
After Viral find out about Kamina's death in Tengen Toppa Gurren Lagann, he's horrified that he's lost the several intervening battles to Simon and Yoko.
- Debatable whether this is an example of this trope. He seems more upset to have lost to a kid than to a woman. Viral doesn't seem to have much of a misogynistic streak if his respect/fear towards Adine is anything to go by.
The latest chapter of Little House With an Orange Roof has Rina bragging that she beat all the boys in her class at arm wrestling. Youta is shown looking humiliated with a note indicating he was one of the losers.
In Codename: Sailor V Takurō Ōtaku refuses to believe his high scores have been trounced by a girl, even accusing Minako of being a man in disguise.

Comic Books

In the Superboy story introducing the Legion of Super-Heroes, Superboy's first task in order to join the team is to compete against Saturn Girl (part of the main Power Trio of the Legion) in retrieving a sunken statue from the ocean. However, Superboy is just barely on his way when he gets sidetracked by a crisis involving the local school's robot Superboy. By the time he resolves it, Saturn Girl has completed the task. When both returned to the clubhouse, Cosmic Boy takes the opportunity to rub it in:

Cosmic Boy: You lost out on your first task... and to a girl! Is this the great Superboy we learned about in school? What's your excuse?

Fan Works

A Very Potter Musical: "We just got beaten by a nerd... Who's a girl."
An all too common a way to demonstrate how "awesome" a Jerk Sue is allowing her to beat up Ron the Death Eater.

Film

Uttered (in almost exactly same words, no less) by one of the heroes of Polish cult sci-fi film Sex Mission, after, well... It (like many other quotes from this film) has since entered Memetic Mutation.
Not beaten by a girl, but The Missing Link from Monsters vs. Aliens isn't too happy that Susan beat the giant robot practically all by herself while he laid unconscious the whole time.

Dr. Cockroach: Poor Link. After all that tough talk, you were out-monstered by a girl. No wonder you're depressed.

When the Dragon/Brute from Dragonheart is mortally wounded by an Action Girl, his response is to incredulously repeat "A girl?!" several times before dying.
The Lion King: Simba gets pinned by his girlfriend Nala on three separate occasions.

Literature

Clan of the Cave Bear had this as a running subplot. Justified Trope in that, to the Clan what Ayla does and is able to do is literally inconceivable.
Averted in A Scandal In Bohemia, Sherlock Holmes, who Does Not Like Women, finds out that the adversary who managed to tail him home, then escape from him, is a woman named Irene Adler. He is greatly impressed and a little bit smitten.
In Half Magic, Katharine wishes to beat Sir Lancelot in a joust, and then has to unwish it when Lancelot is mocked by the other knights because he was beaten by a girl.
In The Bible, we have the story of Abimelech, who was mortally wounded when a woman dropped a millstone on his head. He had one of his men kill him so that people wouldn't say that a woman killed him. Guess what...
In Silicon Wolfpack, Murgatroyd gets KO'd by an Action Girl because she thinks he's trying to steal her car. His friends naturally think this is hilarious, and one of them points out that speed and flexibility count for more than power.
When Margo and Malcolm spar in Time Scout, their first two bouts go to Malcolm. The last two go to Margo. That he, an experienced guide twice her age got manhandled convinces him he hasn't been spending enough time at the gym. That she, too, is spending time there is just a bonus.
The reason why Elend refuses to spar with Vin. Though this has less to do with Elend being macho (he's not, particularly) and more to do with the fact that he's king and Vin is tiny. Knowing full well that she'd beat him, he'd rather not get curbstomped in front of his subjects by someone who's barely five feet... and his girlfriend.
Gerald Tarrand, Villain Protagonist of Coldfire Trilogy is not remotely pleased to learn that the Evil Sorcerer who defeated him in the first book is actually a woman using a masculine title. Of course, the fact that he's a vampire who normally prefers to feed on young women makes it a particularly galling role reversal for him.
In the Encyclopedia Brown series it is a constant source of embarrassment for Bugs Meany that he got beat up by Sally Kimball.
Older Than Feudalism example, from The Bible no less, Judges 9:23-27. Short version, Gideon had a son named Abimelek who decided to murder his siblings (all 70 of them) in order to be ruler of Israel, but one of them, Jotham, escaped. The two brothers fought for control of Israel, Abimelek ultimately winning. Which God did not like at all. So He sent a “spirit of ill will” to convince everyone in the city to revolt against Abimelak. He slaughtered all but a thousand of these revolutionaries, the survivors taking refuge in a tower, and when Abimelak found them, he had his men set fire to it. But as a final act of defiance, a woman at the top of the tower dropped a stone that fell on Abimelak, mortally wounding him. Realizing he was dying, he ordered a soldier nearby to kill him, as he refused to let the records show that he had been killed by a woman. Of course, if one takes the Book of Judges to be a reliable account, this attempt to preserve his legacy failed.

Live-Action TV

At the end of the Doctor Who episode "Utopia", the Master utters his anger at having been fatally wounded by Chantho. His next self is killed in a similar fashion by Lucy in "Last of the Time Lords" and jokes that women often do that.
The Sontaran Kaagh from series 2 of The Sarah Jane Adventures has a similar reaction to being beaten by "a female and half-forms". He survives his first appearance, but feels unable to return to Sontar out of shame, and ends up working for the main villain in the series finale.
In Malcolm in the Middle Reese, gets his ass kicked by a female wrestler in a match, which demoralizes him and causes him to try and be nice, which in turn creates the bully power vacuum that later arises.
The West Wing: An intellectual version- When facing off on Sunday morning talk-show "Capitol Beat", Blonde Republican Sex Kitten Ainsley Hayes takes Sam Seaborn apart rhetorically.

Josh: Toby, come quick! Sam's getting his ass kicked by a girl!
Toby: Ginger, get the popcorn!

Stargate SG-1: A tribal cheiftain, Turghan, gets owned by Carter. And she had a much smaller knife, too.
The whole basis for the "Battle of The Sexists" episode from season 1 of That '70s Show is that Eric can't take being worse at sports than Donna.
Prince Arthur from Merlin is not at all happy to find that the masked figure who bested him in battle was actually Morgause in disguise. He instructs Merlin to spread the word that he purposefully threw the fight because he knew she was a woman.
An episode of Buffy the Vampire Slayer had Xander react with annoyance when Buffy rescued him from a school bully, which is distinctly different and more ego-deflating than the times she saves him from demons.
In an episode of Ned's Declassified School Survival Guide, Mose beats Ned in gym during a martial arts class, causing the local bullies to give him grief that he was beaten up by a girl. Ned seeks the help of Gordy, who simply tells him fighting a girl is a no win situation, as if you lose, you just got beat by a girl, and if you win, you just beat up a girl. In the end, this is resolved by Ned and Mose flipping said bullies to show them how wrong they are.
In Horrible Histories' Boudicca song, a Roman soldier says this.
On The Amazing Race 17, men from two different teams made a number of comments about how they felt of the possibility of losing to either of the female teams, Nat & Kat or Brook & Clair. Thomas, who finished third behind the two female teams in the finale, averted this, as he admitted that the female teams were the two best teams.
- Harlem Globetrotters Flight Time & Big Easy begrudgingly acknowledged sisters Kisha & Jen's racing skills in the Season 18 finale, though their hyper-competitiveness meant they probably would have had this reaction to any team beating them.
- Chip (Season 5) had this reaction after getting smoked by the Bowling Moms in what he described as "putting together a car," but was really just decorating it by attaching a bunch of pieces to it.
Supernatural - The Winchesters are hunting a monster who assumes the form of its victim's idol. Its most recent victim was a teenage girl. The fight ends with Sam cutting its head off and a beat-up Dean on the ground.

Dean: Not a word.
Sam: Dude. You just got whaled on by Paris Hilton.
Dean:...Shut up.

Music

One song by Phil X and The Drills contains the choice lyric "I'm the air hockey champion of the world, of the world ... except for the time I got beat by a girl!"

Professional Wrestling

While not a girl, the principle's the same. Kurt Angle was pinned in his first match against Rey Mysterio, Jr.. After the match, a dumbfounded Angle can only mumble, "I was just pinned by a 12-year-old."

Video Games

In Advance Wars, Eagle expresses his surprise when Sami, who has just beaten his whole army, turns out to be female.
Castlevania: The Dracula X Chronicles:

Dracula: Completely impossible! Beaten... by a little girl?

Seedle from Makai Kingdom was a famous samurai in life, and died when a woman stabbed him while he was trying to rape her. He really hasn't gotten over it, especially since said woman was burned as a witch for killing him and ended up in the Netherworld alongside him, eventually becoming one of his rivals.
One of the pre-recorded taunts in Age of Empires II is "Oh, you just got beaten by a girl."

Toys

In Bionicle Hakann gets beaten by lariska (much to his surprise)

Web Comics

In No Rest for The Wicked, the Boy speculates that some girl beat up Prince Ricardo. A.k.a. "Picky Dick" a Prince Charmless who embodies Minor Flaw Major Overreaction.

Web Original

In The Antithesis, the first episode of the story (I. The Encounter) recounts Alezair Czynri nearly getting killed by Leid Koseling in the battle of Jerusalem circa 1180. Alezair's ego is significantly damaged by this, and this initiates the entire story, making him want to pursue her and perhaps fight her again. Later in Decus, Qaira Eltruan gets his ass beat by Leid on numerous occasions after losing his temper (or after she makes him lose his temper), and often he becomes so impossible to deal with that she must smack some sense into him. This is also ego-damaging to Qaira, since he is what we would deem a "manly-man", also a chauvinist, and also a misogynist. Although the readers find Qaira's beat-downs rather funny, Qaira, in fact, does not.
In the Whateley Universe, huge Montana (who looks like a Sasquatch) gets challenged to a fight by petite Sassy Black Girl Chaka, who proceeds to utterly pwn him. In front of a big portion of the school. This does eventually lower his jerk quotient.

Western Animation

This happens in an episode of Avatar: The Last Airbender when the Kyoshi Warriors jump and tie up the trio, and turns out they are all female.. Sokka refuses to believe that a "bunch of girls" captured them, and tries to argue that "sneaking up" doesn't count as a fair fight. Confronting them later only confirms that they can still best him in a fair fight.
- And then he ends up dating one of them.
Duncan from Total Drama Island was demolished by his own girlfriend, despite mentioning early that he wasn't going to let her win.
Inverted in Futurama, Zapp Brannigan is actually happy when he finds out that the guy who just beat him was actually Leela in disguise. Relieved because he was starting to have... feelings for "him".
In Hey Arnold!, everyone mocks Harold when he loses to Patty at arm-wrestling. After getting to know her, he stops being ashamed and beats up the bullies mocking him.
In South Park, Cartman gets beaten up by Wendy, which causes Cartman to despair that the other kids won't think he's cool anymore. All the other kids tell him that it's OK...they never thought he was cool to begin with!
Imagine the shame of being a muscle-bound henchmen who just got your butt handed to you by a cheerleader, even Kim Possible.
He-Man and the Masters of the Universe: Skeletor responds like this when She-Ra makes her first appearance, and knocks the stuffing out of him: "A female He-Man! This is the worst day of my life!"
This also happens in an episode of Adventures of the Gummi Bears in which Princess Calla defeats every man in a tournament before losing to a masked challenger... who turns out to be a girl as well.
While this could qualify for any villain beaten by The Powerpuff Girls, this explicitly comes up in "Members Only". The girls are not allowed to join the Association of World Super Men because they're girls despite besting the heroes at all the initiation tests. "Mascumax" then pummels the heroes, but the girls defeat him. He leaves crying that he lost to little girls. The association members state that the girls are now their heroes.