"Baby, why do you make me hurt you?!"

If you are being toxic in a game, it is NEVER anyone's fault but your own. Other players can be jerks, it's true! They can feed, they can insult you, they can do a lot of really nasty shit. One thing they cannot do, though, is make you press that enter key and respond with additional toxicity.

If you respond to negative behaviors in a league match, then 99.9% of the time you are being toxic yourself. Don't call people out. Don't insult them. Don't tell other players to report (this is technically calling the person out). Just stay quiet and wait for the post-game screen. File your report without telling anyone, and go on your way. That is, without exception, the only acceptable way to deal with other negative players in your game.

edit: I can see from the down votes that a lot of people don't want to take a step back and recognize their own toxic behaviors