I've been playing Clash Royale on iPad (it's a multiplayer battle game set in the Clash of Clans universe that essentially drops the base building element and concentrates on the strategic combat).

Generally, competitive multiplayer games can be pretty harsh (devolving into toxic) communities. Clash Royale addresses this problem in an interesting way. You're allowed to communicate with your opponent, but only from a fixed vocabulary. There's just no way to be really hostile - the closest it gets is an angry face, which says more "I'm frustrated!" than anything else. There are a few faces and some simple speech -- "Good luck!", "Well played!", etc.

This has a really nice effect - it's actually a pleasant game to play and it's pretty common to get a 'Good game' or 'Well played' at the end, or even during the game when you make a good move. It works well in this situation because it's a 1-vs-1 game -- you aren't coordinating complex actions with teammates, which is where I think something like this would fall down.

Without hostility being in the vocabulary to begin with, you don't really feel like anything is missing and it gets around the whole hurt-feelings problem of 'banning' nicely in this case.