TOXICITY AND CHAMPS
There are many champions in league of legends and thus, it is easy to become toxic due to a number of things etc... One player plays a champion and uses a particular ability very well and thus ruins the game for the opponents One player is very efficient at dodging and thus avoids an ability constantly ruining the game for the opponent.
There are many reasons for being toxin in LOL, as a Darius
main I receive a lot of this toxicity on a daily basis and thus you simply have to live with it and move on....Plus as they say "Everything is better with salt".