When I played mw2 for a short time, (I bought it at a lowered price for the campaign and played it online with friends and when bored) there were tons of them, including hilarious incidents such as a kid saying "I'm gonna lagswitch you all and then you're gonna LAAAAG!" and a douchebag making derogatory comments about some of our low ranks (this being just when we started playing) and when we beat him we sung the lyrics from green day's "homecoming" "nobody likes you, everyone left you, they're all out without you, having fun" over his insults, which made him ragequit. Generally more funny than annoying.
In every other cod i've played, people rarely have mics, even in zombie modes, though I've gotta say, most people who do have mics seem to either be playing music loudly or actually pretty alright people. I just mute the minorities who I don't wanna hear.