What mental disorder is this?

He needs to see a professional in person and have an appropriate evaluation. Anger and sadness can be symptoms of a number of mental health disorders... they can also be symptoms of just being, you know, a person. 

He certainly is "emotionally labile" and jumps from one overwhelming emotion to the other, however you only mention him crying and acting out when he gets angry.

And so the only educated guess could be that he is clinically depressed.

healthy people do not act out with violence or become "psychotic" when they get angry because they have been taught how to control the problem and fix it.  And healthy people do not cry emotionally at the drop of a hat.

Your friend needs to write down his symptoms and see his own family doctor about this.

You can look under manic depressives or bipolar research...

N.Shadows

I'm not a doctor or psychiatrist but it's not schiz  symptoms if you ask me.  He does seem to have some emotional issues but only a professional is qualified to diagnose.  And a lot of the time, they aren't even correct.

from my knowledge, that sounds like BPD.