A couple of months ago a guy did a similar thing to me on Mass Effect 3.
I was playing as an Asari Vanguard for the first time, so I was a little rusty (although now it's one of my best classes), and, yes, I was dying a little bit, but bare in mind I only had like...2 skills. It wasn't as if I was crippling the team. And I wasn't dying THAT much.
Anyway I got a voice message from this other player, but due to it being a multiplayer match I thought I wouldn't check it then. Suddenly I hear him going
"JW. JW. Hey. JW. Hey. JW. Check your voice messages man" - he had any extremely annoying voice. This is no disrespect to Americans, as a lot of us British have annoying voices too, but it was a really whiney American accent. I don't know where from. But it was not a good voice to have.
So anyway, I didn't have a mic so I couldn't inform him that checking my messages would involved me essentially going AFK for a bit. Then I heard him say to his buddy (they were in a clan, doncha know):
"I left him a message....I left him a message that said *chuckles* 'Hey, is the reason you die so much *chuckles* because you don't have a life?'"
I think I found it just as funny as he did - albeit in a different sense. So I quit the game and listened to it, and yeah, "Is the reason you die so much because you don't have a life?". So I messaged him back this elegantly constructed critique of his gameplay and told him that he had an annoying voice, which was what offended me the most. He sent a message back telling me that obviously I had an annoying voice, or else I'd be on mic...obviously.
ANYWAY!
I've digressed. The point is that he wasn't particularly good himself. But the majority of the time these guys that insult other players are dumb arses with nothing better to do. Even if you are genuinely doing something wrong, accidentally, there is no need for "Oh muh gawd yur such a fag!" It's pathetic, it really is. I'd rather risk lightly, accidentally patronising someone and offering them advice then send them a poorly constructed insult made up of very little wit.
People, eh?