I guess that's the thing. It's not something I ever had to personally "grow out of." I'm sure I had my own immature, insufferable moments as a teenager, but I never spouted racist or sexist slurs. That kind of grew out of the general "for the lulz" 4chan internet culture and then just sort of became a...thing for the general younger audience/players.
I wish it was as easy as muting them in games, though. Unfortunately, that toxicity bleeds into the gameplay, too. It's why I stopped playing Awesomenauts. It wasn't just the attitude or language. It was how they'd suddenly play because they were having a temper tantrum. Blatantly letting the other team kill them ("feeding") and not helping at all. Constantly trying to micromanage and criticize literally every move I made, including what abilities I bought. Or constantly talking about how great they are and how bad we are to the point that they just sat in the respawn to "prove it," leaving us at a 2 vs 3 disadvantage.