I actually pissed off a guy once on mic when I was playing Halo. My brother was wanting me to try the multiplayer, since he had just gotten it, and I was in a Oh well, why not phase. My previous experience being more in the RPG/Puzzle Solving adventure type thing.
At first, I was horrible. But by the third round, I started kicking some butt a bit, talking on microphone on it. My voice is clearly girlish, and I had a tendency to giggle if i killed someone.
This one guy thats a friend of my bro kept making a point of saying how i was never gonna be a good gamer and shit, while his other friends were pretty accepting. During that third round, i kept finding that same guy. And shooting him. And giggling.
He went into this t rex type roaring phase, about how he was gonna kill me then teabag me and whatever, but he never got a shot on me again. XD after 2 more rounds of that, he left.
No one else was upset when i killed them, btw. And thats the thing. There will always be some idiot nutjob that chooses to play multiplayer while being incredibly sexist. Just like there are all sorts of idiots in gaming. I believe girls can be good depending on the game, and i have no problem with either. And neither does most of my friends, or my brother's.
You just have to shoot down the occasional Jerk.