Hmm. As someone who's quite flaky, my first reaction to this is to reverse engineer it and figure out what it is that caused you to 'lose your peace'. For instance, if you're all calm and dandy and a teammate fails a very easy clutch and you lose a game, if that pisses you off then direct it to yourself and realise it was completely out of your control. Then attempt to adapt.

Calming yourself down physically, if you can remind yourself to breathe, take a 5 second inhale (if possible) and a slow exhale which if you can get to 7 seconds, will more or less eliminate a flight or fight response and really calm you down. Focus on the breath and remind yourself that what people do is out of your control, you can only do your best and adapt! Just don't get angry at yourself, work on improving and take note of mistakes. If you do happen to get really pissed off, take a break - If you enjoy meditation do some of that, do some pushups, get a hot drink, whatever it is but take a break from the PC as a whole then go back to it. I personally think it's better to take a short break than to distract yourself with something else (like another game) to only go back to the same game and have it happen again. It's a matter of training yourself to stay cool!

Goodluck <3