So angry

I have this "friend". He attention-seeks more than anyone I know and it annoys EVERYONE. E.g. I make a joke about having too much caffiene. The weekend after I discovered proplus, he comes in saying he ate and entire pack of caffiene pills and collapsed. I know this isn't true because a) his mum and mine tell each other literally everything; if anything happens to my parents I will go to his in their will and b) today I took twice the recommended dosage and he told me how bad that is, before remembering what he had claimed and saying "it cant be as bad as me though"

Anyway. Onto the reason I am fuming. Basically, last year he used to go between different groups of friends until he pissed them off. Then he would stick around with me. Then find a new group of friends and revert to taking the piss out of me again. As it turns out, after falling out with someone, he self harmed FOR THE SOLE REASON of making this person feel bad. And the worst part is, I cant even be mad at him, because then people will ask why, and if I tell them they would ask why I care, self harm is stupid, then the awkward questions begin. And I cant tell HIM why I'm mad because he will just say "you dont know what its like" yada yada yada
I'm so mad