PSA: A lot of kids play this game.
I started playing ranked when I was 12 in middle school, and I had a lot of friends of the same age that I played with. I was really bad at the time (500 elo) and I had a lot to learn and I did a lot of stupid things.
Especially in ranked, please understand that a lot of "trolls" or people who are really bad at the game are probably 12 or 13 a lot of the times. So you need to talk to them like they are 12. You wouldn't tell a 12 year old "go kill yourself" to their face, so don't do it in game either. Just be patient.
EDIT: I'm not condoning 12 year olds playing this game, I'm just saying don't cuss them out or try to realize they are probably just kids.