It relates to our primate past when throwing faeces at someone was considered funny. This slowly evolved into hurling disgusting insults excused as "humour". Apparently what's humorous to a sociopath is not funny to normal people.
I have seen this phenomena many times. Its funny to be rude and insulting? Not in my book. I'm merely observing a lower primate consciousness.
These days the meaning of being "politically incorrect" is to be rude, insulting ad racist when in actual fact being politically incorrect does NOT mean that. Plain vulgar rudeness and bad manners is not being politically incorrect; it is just gutter ethics.
Who finds it funny: rude vulgar sociopaths who don't possess empathy.