I think giving them a "behavior detrimental to the board" line would be bad, actually. Being specific helps, and so too when we can point to history of past issues and chances. It makes it clear we are banning according to protocol.
Using a catch-all "behavior detrimental to the board" and leaving it at that will be read by people, including the rest of the board, as "I'm the admin and I say so." Which is the reality, but it won't make people very happy, or want to be here. We come off as heavy-handed and capricious when nothing could be further from the truth.