I used to be a toxic flamer
I now learned that the best way to deal with people who insult you is not to reply, as tempting as it is. I remember myself stating to people to uninstall and simply "you f@#!ing suck", :"f#$@ you", or "stfu." This is big change for me, and it made games more enjoyable. Rather than blaming teammates, I try and help them.
It is definitely possible to stop being toxic, even if the game itself can be seriously frustrating.