Smash and Mario Kart

The first thing that comes to mind is Rust. A game where you could leave other people alone for most of the time you play, and suffer very little... becomes a game where you almost can't play at all when very serious and dedicated players step in.
I choose not to use "Toxic" or "Tryhard" because well... people just playing the game can appear that way to anyone not on their level, these labels are little more than wasteful hateful terms. ;)

There are few games that will make you question your overall choices in life, more than Rust.