I'm a girl myself and I play zombies mostly, not a fan of Black Ops multiplayer to be honest. My ID isn't obvious to the fact I'm female, but after games of zombies I get friend requests and they get chatting to me. Somehow it steers towards my gender and when it comes out I'm female, they suddenly turn nasty and sexist. "No way you can't be a girl you're too good!" or "A girl can't be better than me!!" are just some of many remarks I've received. Some refuse to believe it or others get very creepy and declare their love for me (lmao). I rarely find players who are actually "respectful" about it.
I also play MW3 and I have seen some "G!RL" clan tags, but on mic you can hear they're male. Even being a girl myself I don't always trust that someone who has "girl" in their tag or ID, or a "girly" callsign, is definitely a girl. But, to be honest, I don't care what's between their legs as long as they play and don't take themselves or the game too seriously!
Add me if you'd like SHOTnSKILLZ! Sorta a newb =P but I am becoming increasingly obsessed with bops2!!