Friend wants to Fight someone I know.?

[Jiba jabba]

Ok so this kid in my class got beat up by my friend. Now this kid is REALLY REALLY annoying like he says the most grotesque things....everything about him is repulsive.
So in my class its pretty lax, all we do is build stuff and talk...I brought up my friends name and he starts getting red in the face and says crap about him, he even told me to tell my friend..which i did......

So my friend calls him out, and he denies everything then my friend makes fun of him some more. Then the next day I question him about it and he starts yelling in the middle of class at me....so i just start laughing at him. I really would have liked to back hand him straight in the mouth. But i wouldn't disrespect my teacher like that by hitting him in the middle of class......

So what would you guys suggest i do if he raises his voice again like that?