What if you put in some logic so that, when someone says to start the game, and if both of these exist:

-Human players slot count is greater than 1
-Overlapping key maps exist between the active human player slots

A window pops up saying that conflicting key maps exist and you need to fix them before you can play.

That would be better than leaving things as-is, but I think it would be best (and also easier!) to pick some better default hotkeys. It's probably not possible to find reasonable hotkeys for four players, but there's no reason we have to do that. My recommendation would be to lower the maximum number of human players per game from four down to three.  Worm two can use wasd and worm three can use hjkl: https://en.wikipedia.org/wiki/Arrow_keys

Closing all the bugs. A major rewrite of the code is landing for 3.20, and there's no point in worrying about bugs in the old version anymore.