I ban them when they get reported several times for the names. Some are coming back again under slighty different names, there are so many variations on just "Hitler", for example, that are easily recognizable for a human but not for an algorithm. Same for "Black Lives matter" variants trying to subvert that slogan.
The truth is that for some people "fun" includes having provocational usernames, be they sexual or political or otherwise. I don't think there is a consensus on where the border is between "still OK" and "to sexual/political". As I said, I ban what is clearly "too much" to me, which of course is highly subjective.