A law (especially prevalent in Sitcoms): If you're male and under 11 years old, you have to automatically think romance and females are gross. Girls of the same age sometimes claim that boys have cooties.
For those of you who were wondering, there are such things as cooties, and they're not limited to girls. "Cooties" just happens to be another word for "body lice."
It should be noted that Cooties is generally only something that happens to girls their own age. It rarely, if ever, affects older girls. In fact, a boy can think that Girls Have Cooties even while having a Precocious Crush on an older girl or woman.
Arguably becoming a Discredited Trope as in Real Life young boys are just as likely to boast about their "girlfriends". This may or may not be due to the increased prominence—compared to a generation ago—of romance and sexuality in entertainment media aimed at or enjoyed by kids. Often leads to jokes about STDs.
If the boy does not get over his dislike of women when he grows up, he might be a He-Man Woman Hater. Compare Allergic to Love.
Mahou Sensei Negima!: Negi's friend Kotaro plays this fairly straight (especially the romance thing), with a few exceptions in his adoptive sisters and girls who can fight. That said, he still thinks kissing is gross.
The Frantics sketch "Outgrossing" invovles two boys trying to out-gross each other (turning their eyelids inside-out, etc.). A girl comes along and says she can out-gross them both, which they have a hard time believing - until she describes exactly how.
I can kiss you! And I can be your girlfriend!
Franklin Richards, Son of a Genius (who must be 6 or something) initially rejects Katie Power (same age) specifically because she has cooties. In a different universe of the multiverse (I think), Katie Power from the future tells Katie Power that Franklin Richards was her first boyfriend; young Katie insists that "boys are gross" but future herself calmly tells her that, in a few years, she'll change her mind.
Being a small puppy, Scamp usually doesn't like girls (especially not his sisters), although this varies depending on the writer.
Damian Wayne (Batman's biological son) turns up his brattinessUp to Eleven whenever he deals with Batgirl or Supergirl. Both of them are blondes with blue eyes.
The dusty blue-haired boy gave Matsuri a skeptical look, and with great decorum noted, "Icky."
Played With in Joe's New Look when Silvia refuses to put on Joe's battle suit, finding the idea of her wearing male clothes scandalous. As Joe's already unwillingly wearing Silvia's garments, he isn't happy with her reaction.
Simba and Nala from The Lion King don't think the other sex is "icky" but as cubs they don't seem to like the idea of them being mates due to this.
William Brown in the Just William books can be quite the KidAnova with his chivalrous pining for Girl Next Door Joan and susceptibility to pretty actresses. But Violet Elizabeth Bott leaves him shaken to the core:
I'm not going to have anything to do with any old girl ever again,' said William.
'It's all very well saying that,' said Douglas, who had been deeply impressed that morning by the inevitability and deadly persistence of the sex, 'it's them what has to do with you.'
'Well, I'm never going to marry any old girl," said William.
'It's all very well saying that,' said Douglas. 'But some old girl is prob'ly going to marry you.'
In Artemis Fowl and the Time Paradox, 10-year-old Artemis says of Holly and 14-year-old Artemis kissing that you wouldn't catch him wasting time like that. Not as vehement as some of the other examples, but does contain built-in proof he'll grow out of it: Within three years, back in the second book (or at least non-U.S. editions thereof), he's consciously aware that he'll be attracted to Holly when he's older.
The book No Talking by Andrew Clements features an entire group of children who are said to be at the point where they should have gotten over this, but never did. In order to try to prove that one group (either boys or girls) are better than the other, they stage a "no talking" contest. In the end, the group largely learns to shed the "cooties" concept.
In The 39 Clues. Dan seems to think this. Example: in Book 5, when he is doing something immature and his sister Amy says something to the effect of, "This is why you'll never have a girlfriend," he replies, "Like I'd want one!"
"I know that's redundant but otherwise it doesn't spell anything. Now go away."
But "Get Rid Of Girls" doesspell something. Just not something he should be thinking about.
Calvin also notably attempts to see movies like "Vampire Sorority Babes". He might just be overacting to shut Hobbes up about Susie.
Calvin wants to see the movies solely because he knows they are considered "grown up" and "naughty"; he never displays any understanding of why those sorts of movies are considered "grown up" or "naughty". (He once asks Hobbes what "contains adult situations" means; Hobbes says that the movies show people paying bills, going to work, etc., and he's always wondered how movies like that make any money.)
Dennis the Menace was once called on this in a late 2007/early 2008 strip, and admits it ... except that he's fine with his mother, Mrs Wilson and the local tomboy.
Jason from FoxTrot is an odd example. He started out firmly in this trope, but a couple of decades of extremely subtle Character Development due to his sorta-friendly relationship with Eileen seems to be weaning him off it. Jason still would rather be caught dead than be known at large as being her friend, but he's not quite so adamantly paranoid about it recently.
Marcus, on the other hand, started firmly in the trope, but seems to have thrown it off completely.
Averted in the comic strip Heart of the City, where Dean is Heart's best friend and frequent partner-in-crime. He's generally more befuddled by girls than disgusted. (Heart's occasional declarations that Dean's her boyfriend draw a bemused "Um... okay" as often as not.) One New Year's Eve, he actually dressed up in a tux and and announced that to celebrate, "I thought I might hang out with the prettiest girl in Philadelphia." Making it clear that, yes, he meant her.
The title character in Agnes has the "boys have cooties" variant, although she still engages in a kind of passive-aggressive flirting with a boy at school named Bob.
The show Sonic X is notable for zig-zagging this trope. He gets defeated in a match when Rouge kisses him on the cheek, grossing him out and playing this trope straight. Then subverted when he gets a love interest in a plant girl named Cosmo in the third season, though it ends very badly.
Women are crazy... for Dr. Tran, who says "Girls are grody!" This doesn't stop a great deal of "Tran-sexuals".
Original Life did a whole storyline about cooties, starting here, and it's monstrously over the top.
Ozy and Millie goes there, too. But not without some fun. Felicia's response to Millie touching her after being 'infested' by boy germs from Ozy? Runs away screaming for various cleaners, culminating with 'Heck, set me on fire!' And you thought it was useless..
Ben from Ben 10 believes this throughout most of the original series (as he's a teenager in Alien Force, he's outgrown it). He does make an exception for Kai, an Indian girl seen in one episode... but Kai takes his attention and runs with it... to creepy, creepy places.
In the Codename: Kids Next Door episode "Operation OUTBREAK", Sector V is sent on a mission to decontaminate the organization's underwater research center from the much-feared Coojatisnal Octo Oogie Terta Infecto Epi Streptacaucus.
Also subverted, once the team finds out what they're dealing with (an operative's kid sister), they think said operative is nuts for calling them.
Cooties actually appear as girly butterflies which inhabit DeeDee's bedroom in Dexters Laboratory. Dexter himself greatly fears them.
Ed, Edd n Eddy This seems to be one of the main reasons the Eds flee from the Kanker Sisters. This doesn't seem to apply to pretty, girl-next-door Nazz.
On The Penguins of Madagascar, the zoo animals see some children talking about cooties and are later convinced that Marlene has caused an outbreak of them after they start getting itchy. Turns out Marlene had mistaken poison ivy for a moisturizing plant and had unwittingly spread it to the others.
Inverted in the The Powerpuff Girls episode "Cootie Gras", where our kindergartener heroines are terrified of a boy said to have cooties. Mojo Jojo uses this fact to keep the girls at bay until they get over it. Once they do, however, they leave him Covered in Kisses, then go kick Mojo's butt.
In the episode "Femme Fatale", Bubbles says that boys "are worse than their cooties".
Also, used in the first episode featuring the Rowdyruff Boys: The girls' key to defeat them is to look prettily at them and actually kiss them... and it works so well the guys explode in horror. Lampshaded right after this, when Bubbles and Blossom think kissing isn't that bad, but Buttercup is shown coughing and almost throwing up in disgust.
Note that in their second appearance this doesn't work, as Him had given them a "cootie shot."
The Simpsons, because of Negative Continuity, is all over the place with this one. Bart will go from apparently genuinely thinking girls have cooties, to making out with a girl, and then right back to thinking they have cooties.
Played with in one episode. Bart has asked Ralph and Milhouse to sweep up the leaves in the garden (they're presumably getting paid). Then Sherri and Terri come along and ask the boys if they want to play with them. Bart refuses and gives Ralph and Milhouse their "cootie shots". However, when Bart sees their cousin, he's more than happy to play with them.
The South Park kids have managed to maintain this for quite a while, except for Kenny, who appears to have been horny since age 8.
Not really; what about Stan and Wendy? Usually the other boys just think it's stupid to be so interested in girls, not bad per se. (This, of course, changes when they get a Girl of the Week.)
Beverly Hills Teens: Normally averted with Chester, who is quite interested in female attention (and gets much more than some of the older boys). However, in one episode Jillian responds to a remark about "embracing" boys with "how totally yucky". She changes her mind after a few minutes, when she is thrown into the air and Troy catches her.
Truth in Television for both sexes in many cultures and environments (remember the cootie shots?), but the behavior tends to disappear around fourth grade. The general feeling and how early or late it tends to disappear, however, vary across cultures.
Even once it disappears, there's a clear boy/girl divide usually until around the middle of Junior High. Until then, the boys and girls typically sit at seperate lunch tables, engage in seperate activities at Recess, etc.
An article some years back (no link, sorry) about Tamora Pierce played with this trope with an anecdote about the author's eight-year-old son, an avid reader. It was Mum's job just to bring home the books. At one point, Mum noticed that the pictures on the cover were of girls. Not boys, not animals, girls. She asked his son, "Is this a girl's book?" "No, it's not a girl's book," replies her son with all the scorn of an eight-year-old boy. Then he says, "It's about a girl."
Later on in the article, the book's author (Tamora Pierce, of course) mentions that parents have thanked her for including the subject of girls' periods. "Hmm, Mum didn't know that."
Cooties can be used as a slang term for head lice that can be caught from people of the opposite sex.
A humorous Gender Flip occurred during the filming of Interview With A Vampire, when eleven year-old Kirsten Dunst had to kiss Brad Pitt. Most women would have sold their souls for a chance to do it, but Dunst was apparently grossed out by the thought of Pitt having cooties. It turned out to be much more pleasant than she expected.