WFT's wrong with ppl????

I'm so angry I could burst right now!! My best friend'd had a thing going with this guy for a couple of weeks. They seemed like they would really get serious, whe he suddenly started acting like a total asshole!!

Yesterday me and my friend rented a movie, and she sent him a text asking if he wanted to come watch it too. He answered that he was tired and didn't really feel like it at the moment.
My friend thought she'd tease him a little bit and wrote back "Ok, then I'll just have to snuggle with Markus instead Not as nice as with you though, but.. "

Markus is my nickname, although it's techincally a boy's name, and she'd mentioned it a few times before around him, referring to me as a "she" even though she called me Markus. He didn't say anything about it and she thought that he got the fact that it was my nickname and that I wasn't really a boy.

Apparently not. Now he refuses to speak to her and just now sent a text to her which said "Can't really bother with you right now, I'm snuggling with Johanna.."!!!

I bet he doesn't even know a girl named "Johanna", it's just to hurt my friend! She got really upset and started crying, and that's the first time I've ever seen my friend like that!

I tried to call him and explain to him what it all had been about, but he just hang up on me! >I even said it was me who was "Markus", and he should've heard on my voice I was a girl, but he wouldn't listen..

Now he calls my friend a liar and refuses to talk to her.....

I don't know what to do.. Why the fuck do guys act like this??? My friend really got hurt by the things he said, and it really upset me too!! My friend is like a sister to me and I don't want her to get hurt....