Think Season 5 has been the most toxic season I've ever played in.
And honestly, the removal of the tribunal is probably to blame here, as well as the automated banning system either not working properly or being too soft. I honestly don't know why no one has mentioned it, but the removal of the tribunal means only Riot handles the reports of toxic teammates and not the community. This really puts too much on Riot's plate to handle and therefore, I think bans on toxic people have dramatically shrunk. And some people have talked about getting messages that their reports got someone banned, but I've never received one, and I guarantee you I've reported countless people who deserve to be banned. The toxicity is ridiculous this season, and I really hope Riot either revamps the Tribunal or actually get to work on bans. I used to see toxic people every 3-4 games last season; now I'm seeing at least 1 every game.