"All right. Got my Xbox 360 set up with Live and I'm ready to play. Wait, what's this? A mic? Why would I need this? Besides, mics are for noobs who aren't MLG like me." or "Sweet, I've got my Kinect set up and know how to use it as a mic. Now all I have to do is turn my TV up on full blast and start meeting people." and of course "So I'm ten years old and probably shouldn't even be playing this game, I'm sure no one will mind. And just to be sure everyone can hear me I'm going to talk really loudly and have my mic practically right the mouth mouth that I breath loudly through."
Seriously, the Xbox comes with a mic. That means you should use it, but keep it out of your mouth so that we can't hear you breathing all the time. And while the Kinect may have some good audio quality when used as a mic, if you have your TV up it will echo and no one likes that. Not to mention most of the time all that others hear is a metallic screeching and anything else going on in the house.
Almost forgot a few.
"I'm so MLG, I don't need to use teamwork to win because I'm so awesome that I could do this by myself. I think I'll also constantly brag about how awesome I am and how much everyone else but me sucks. If we lose I'll just blame it on every one else sucking and not on the fact that I wasn't even trying to help complete the objective." and " Because I secretly suck at this game, I'll just use a lag switch/mod so that I can avoid being shot/take several usually lethal hits and keep on going/always hit someone even if I'm not pointing at them just to prove how good I am. If anyone should figure out that I am cheating and actually accuse me of it, I'll just laugh at them while I say something like "I don't know what you're talking about." or "U jelly?" because I'm so awesome."