Happy New Year, and don't forget...
It is very unlikely that your teammates are actually "retarded". If they make a mistake and you lose, well, it's a team based game and your teammates are not robots.
You may be competitive and playing to win, but if you lose because of someone else, why would you rage? You know you played well. If you're leading a Nascar race and your car breaks down and you finish last, nobody you care about is going to blame you. People who do just look at your division and judge you based on that aren't worth your time, so don't waste any on them.
The only thing you achieve by raging at a teammate is that he's going to be angry and rage at the next team and the next and the next and eventually someone is going to be angry back at you. In 10 years' time, you won't give a crap about your exact division in 2015, all you'll know is "I had some fun years with League" or "I hated every single human being in League".

Happy New Year!