Courtesy, common sense, and a modicum of respect. Simple, and maybe too broad for some to cope with.
Are there gray areas? Certainly.
I have said this enough in enough threads that it is time to take the next step. Locking threads is no longer a good option. The abusers continue to abuse, whether its through trolling for the sole purpose of antagonizing all the way to flat out obnoxious behavior which contributes nothing to any discussion.
No matter what a moderator does on a bulletin board, it is a no-win situation. It's a very irritating situation to be placed in, but there are those that take great pride in placing moderators in that situation.
You know, it really is quite trivial to have a serious discussion about controversial topics, without resorting to abusive behavior. Abusive behavior comes in many forms. It is not always about the words used. There are people on this board which appear to be very content with simply antagonizing situations.
I get no joy out of this. It takes away from the community for me to spend the amount of time I spend monitoring the board. Time better spent working to improve the service HTC offers.