I'd rather tell him that the things he's insecure about are obvious to all, and that everyone knows he's pathetic in spite of his efforts to hide his true nature. Physical violence is for bullies who are uncreative. I'm meaner than that.
I would prefer to hurt him by breaking down that narcissistic facade and exposing him for who he really is. Or a Mach Punch from a Machoke. That would work too.
