Heh. No, that actually sounds pretty fair and true-to-life. Just think of it as the emotional version of the arm-punch. If you punch a stranger in the arm, that's not cool - a punch is inherently an attack, and hurts, and that's not something you get to do to people you don't know. If you punch your best bud in the arm, though, that's a sign of affection (if you have that kind of relationship, at least) - a punch is still inherently an attack, the purpose of which is to cause hurt, but because of the context and your relationship to your friend, the hurt is removed and the meaning changes. If your two characters are close, they might easily beat on each other verbally in ways that wouldn't be acceptable between people who weren't close, and that wouldn't be offensive because it's clear neither of them is truly hurt.
(There are still lines, of course - you don't get to knife your friend, and your character is probably not going to call her roommate a faggot. But "lesbo" is pretty far on the innocuous side, so I wouldn't worry about that much at least.)