Blatantly Disruptive Posts
Blatantly Inciting Anger
Racism would fall under both of the above. But we've hesitated to try and form a specific definition about what racism is because its so broadly defined in so many different ways by so many different people.
The DGN rules are left a bit "generalized" so that they can be enforced with flexibility.
Many of the few people that have been banned over the 5+ years DGN has been around , has been due to continued racist remarks. (rare when anyone would get banned for any single comment, usually is due to them not curbing or cutting out their negative behavior after being asked at least once to stop)
Blatant, clear examples of repeated racism, and direct repeated examples of directly insulting other posters are two key reasons for most of the bans in the past.