Best Friend trouble... PLEASE HELP!!!?

[Tyler R]

So if your best friend says he is going to go Anorexic and then blame his death on you, would it be right to hate him? I jokingly called him anorexic in class one day and he freaks out and I get a message from him at one in the morning over Myspace saying he was going to go Anorexic to prove that he wasn't right now. And that if he died it would be all my fault...
This isn't the first time he has pulled something like this, it has actually been continuous over our 8 year friendship... Later he referred to our friendship as being all a game to him... So do I have the right to hate him for this? Or what should I do...

Another side question: He has found a new 'best friend' who also happens to be one of my friends as well, so should I warn her that this might happen? Of how much he loves drama and will go through times when he wont talk to her for long periods of time (once it reached 3 months) Should I tell her? Or let her find out on her own?