So let's see.
Harry Potter fandom is the biggest, baddest bully on the block. He actually attracts the attention of not just the principal, but law enforcement. People worry about him bringing a gun to school and shooting everyone one day, but that's just silly--with all this attention, he has exactly what he wants. No need for shooting sprees when he can grab a nerd and shove their head in a toilet bowl any time he wants.
Fullmetal Alchemist fandom is that seriously unhinged kid who runs around setting things on fire. It doesn't matter how many times he's reprimanded for it or how many psychiatrists he sees. He just likes seeing that puppy burn.
Naruto fandom is a wannabe bully. He picks on the nerds and sometimes threatens them for their lunch money, but he can't bring himself to actually use violence. Secretly, he actually does really well on his schoolwork, but he's embarrassed about it and doesn't want anybody to know. More than that, though, he doesn't want anybody to know that he's gay, so he constantly picks on smaller kids that he thinks look gay. "Fagwad" is his favorite insult.
Bleach fandom is the teacher's pet. She's sweet and smart and active and everyone's sure she'll get into Princeton. But once people get to know her, they realize that her personal beliefs are pathetic and uninspired. To cope with this emptiness, whenever she goes to the school restrooms, she takes with her a Sharpie and writes vicious insults on the stall doors about the sexual proclivities of the rest of the students and some of the faculty.
House fandom is that smug bastard who's watched Monty Python and read Discworld and thinks this makes him ten times more clever than any other teenager in the entire world, or at least the United States. He will never pass up an opportunity to throw some jibe that he's sure is astoundingly clever at everyone else. They just wish he'd shut up.
Gundam SEED/Destiny fandom is a popular cheerleader with a great smile and an even better rack. Anyone who actually bothers getting to know her, however, will discover that she's all body and no substance. She'll probably die of a drug overdose at the age of twenty-five. It won't even be a very good drug.
Final Fantasy fandom is that unwashed nerd who comes in every day and sits at the back of class reading comics and giggling in a way that makes him sound like he's snorting. He mumbles to himself a lot, stares around nervously, and may actually have genuine mental issues, but nobody cares, because he's just so fun to laugh at.
One Piece fandom happily goes to school, does his work, and gets on just fine, because he's wearing headphones and listening to happy music the whole time, allowing him to ignore all the other losers.
Someone should write a fanfic featuring these characters. It would be the best fanfic ever, or at least almost as awesome as this one.
NOTE: I mock because I love! Except SEED fandom, because I'm a horrible, no-good, Fllay-loving, Neo-bashing Fukuda-hater. Bring on the Swedish trolls!