Do what a couple of us did on TS one day, and play the compliment game. At the beginning of the next round, you compliment the person who killed you, in a completely non-sarcastic, genuine way. Hahaha, it comes out hilarious, a couple people were getting really into it.
I know what you mean though. I'm a positive guy too, try my best to be honorable and humble even to strangers on the internet, but I told them if I had voice activation on they'd worry about me.
A large part of it is day to day stuff too. Not to blame it on the time of year, but we do tend to set the bar pretty low for ourselves and let things slide, stagnate, and build up. I notice my language has taken a serious turn for the worse, and big deal right? Our words mean stuff though, they really do.
Maybe step away, do something IRL for a couple hours that relaxes you. Realize we've all had humiliating experiences and not everyone's as big an asshole as they really act sometimes. I know I haven't played on an alt in ages, that would be fun to do to take things less seriously and play the game from a different angle. Try something new, and realize nobody looks above or below their own name on the scoreboard, and the game is full of horseshit and goofy mechanics. Its the price to pay for international multiplayer.