As found by coincidence by Hannibal_Barca last christmas (#4433), when sending someone a special character that is not supported by our utf8 code,
a debug breakpoint will be triggered. This character can be posted in the lobby to selectively or unselectively crash players.
It was briefly discussed in the staff meeting on April 9th 2017:
20:50:29 <Itms> elexis: for the crash, I think in this low level code, a safe thing to do would be to replace the character by one inside the BMP (maybe a square) and print an error
20:51:30 <elexis> yes, but it would remove the ability debug it, for example not show a stacktrace anymore
20:53:34 <elexis> and there might be many more places where debug breakpoints could be triggered for players other than the local one
20:53:49 <elexis> so a more general question might be whether we would disable breakpoints entirely for releases
20:54:42 <Itms> elexis: there is nothing we can do here except supporting utf8 chars outside that plane (which would be great but might never happen)
20:55:03 <Itms> elexis: and for releases, I'd say not for alphas or betas ^