Kai
For boys? He's consistently aggressive, constantly picking fights for the sake of gaining some form of dominance. He hates losing (even though it happens with relative frequence), he's stubborn as can be, and more often than not, he believes he's right. Even, often enough, about things he doesn't know about.
For girls? It depends. Sometimes he can act rather a gentleman, but other times his more aggressive side comes out, and he can be rather demanding around the 'weaker sex'. Someone's always welcome to knock him down a peg or two, but even then, good luck getting him to change his mind very far.
Also he's going in the dorms since he'd otherwise be homeless, so he'll probably need a roommate (insofar as few would probably be able to tolerate him).