Is calling your own best friend stupid, or just making fun of their own forehead a sin?

I have a best friend I always call online, and for some reason he just starts to call me stuff like "idiot", "stupid" etc. And it kinda does go on my nerves, because I did discuss about it to him, that it's not being funny anymore and just a thing that makes us more separate. I'm a type of guy that would never leave a friend, or even block them, and he always blocks me for a few days and just randomly unblocks me and completely ignoring the fact that he blocks me like almost every day, which does pisses me off, but I control it. Forgot to say he is muslim himself and I am too. Idk if he has anger issues and stuff like that, and i'm afraid of how this is going to end up with if he keeps doing the same thing and just slowly getting worse day by day. Sorry if I don't make sense.