Bad games happen. Don't let them phase you.
Bad games happen.
http://i.imgur.com/4oaWprN.jpg
They make you want to rage.
Call me a pushover, or a kiss-up, or whatever you want, but in my humble opinion, when teammates have bad games, no matter HOW angry I am at the other players, and no matter HOW badly I WANT to tell them they're upsetting me by their poor play, I find myself typing "It's okay" or "Don't worry too much about it, everyone has bad games." I may mutter something to my roommate about how they're annoying me, but I never say things like that in my games to the other players. And the result is that when the game ends, no matter how badly we lose, I'm actually not too mad.
There's no strife. There's not much tension. Despite playing poorly, in the end, everybody is (for the most part) in at least slightly better spirits because at least one player was trying to make the environment positive.
It seems worthless sometimes, and it seems like there's no point, because others will still get angry. But for me, it's changed my entire outlook on games. I don't mind losing ranked games nearly as much. I understand, and believe, and no longer get mad at "bad teammates," because I know bad games do happen to everybody.
I enjoy the game so much more now, both when I win and when I lose.
Try it. Try, for just 5 whole games, not saying a single negative word about another player's performance, and when somebody royally ****'s up, say nothing but "It's okay man. Next time." Your teammate will play better, you will play better, and both of you will feel better.