It normally starts when someone says "I don't think I was being unreasonable"..
Truth is on every forum there are some bullies, and most of the antagonism centres around them, they either get wound up or wind others up in a bid to inflate their egos, its jsut a pissing contest. (on here I'm one of them, but in my defence I only bully the bullies or deride the trolls.)
There will always be few who feel a special affinity to a particular forum and appoint themselves forum bully. There's a couple on here. On other forums there are more, and I know of one forum where there are none, but that is particularly well moderated.