Easily Rocket League. It's always been toxic but it's been much worse since becoming free to play.
- Rage quitting
- Malicious compliance (AFK, accidental own-goals)
- Team mates playing for the opposing team entire games
- Passive aggressive quick chats
- Overtly aggressive free-form chats (being chastised over every tiny mistake)
The game's competitive ranking systems makes it so each win and loss matters, and people often take their vitriol out on their own team before looking inwards.
Having worked with the Mint team directly in the past, I can assure you LMDE is last priority for them without as much polish, as it exists as a backup option in case something happens to Ubuntu. This boils down to Ubuntu vs Debian with some mint userland on top.