Strategies to calm down? Firstly, what kind of person are you? Are you prone to things you don't understand? Are you prone to things being too inefficient for you? Or are you prone to dislike everything that is not like you?
If you are someone who don't understand things and go off on spouting your unwelcome opinion on others, then you have to just stop typing, literally. Don't communicate with anyone on what is on your mind. Stupid makes stupid.
If you just hate anything inefficient enough to match your abilities, then you better lead by example. If you are inept at leading then you might as well suck it up and finish the match and accept the outcome.
If you really just hate everything that is not you then you should really uninstall league of legends and go play singleplayer games.
So, which are you?