For when an operator isn't in the room and the offender's actions aren't quite reportable:

/personalmute [username]
/pmute [username]

A common feature in most MOBAs, it simply stops any of the pmuted's messages from appearing on your screen. Doesn't require any sort of special permissions, as it doesn't interfere with anyone else's communication with the pmuted.

One might argue that you could just create a new server to play on in order to avoid unwanted messaging, but player-created servers often don't draw nearly the amount of attention that the permanent public servers do.