Like a Trust Fall, a Trust Punch is when one guy (or girl) goes up to another guy and proceeds to pretend to punch the guy in the balls while declaring, "Trust Punch!". If the guys flinches or blocks the pretend punch then he does not trust you. The point is to pretend to punch, it must not be a real punch.
Guy 1: "Trust Punch!" *Proceeds to pretend punch guy 2 in the balls*.
Guy 2: *Flinches* "What the Fuck!"
Guy 1: "You gotta trust me bro."