how do i stop bein trash at this game
stop believing what other people say about you and play. sure you (and this is referring to anyone reading this post) might actually be bad, or very good. who cares, if you feel yourself are bad regardless of this, then improve.
if some jackass makes fun of you in like atleast 4 different ways, ignore him and keep trudging on until you're good at some champion or a lot of them.
mute the entire match if things start going south, it's not worth the negativity that might come out as much as people like to believe otherwise
work on map awareness and item awareness, your builds should always differ depending on the enemy team