Simplest solution when this happens. Don't take the bait. In simple words, not to get provoked. Mature members would very well know about this and can easily ignore such posts and/or posters.1) Provocating posts.
Mature members again would not sink to this level of course, but you cannot stop people from doing that. Making a rule against it would be like against freedom of speech. If there is indeed something vile and offensive remarks, the moderation will take care of it.2). Discriminating post.
Again, the moderation is there to take care of it.3) Humiliating posts.