Heres some context

My relationship with this friend prior to this was already not that good because he always makes these racist asian jokes when I join the call and would continue making them when I'm in the call. Also he would keep moving me around the calls on the server so all I do is take his roles away for literally a second and give it back, but he always gets angry and just leaves.

One day he decided to go to the afk channel with these 2 other guys and unmutes themselves to talk. I saw this and I tried moving them out but they keep joining the AFK channel so I just server muted them until they moved out. The other two didn't really mind but the "friend" started calling me a cunt, asshole, and bitch on DM. His main argument is that this is a casual server with friends so he should be able to talk in AFK, and my main point is that this isn't a big deal: I've unmutes him and his friends and he can just talk on any channel on the server except for AFK, since that is for AFK people only. After some arguing I said "maybe the autism is getting to you but you should just relax and reflect on this when you've calmed down." 

Remember, this guy has a history for dark and racist/offensive jokes/speech style, so I thought simply saying he's autistic wouldn't be much of a deal. (He would joke about down syndrome, autism, Asperger's, all kinda stuff all the time)

AITA?