When your natural resting expression appears so angry that people who do not know you, and even those who do at times, believe you may soon murder someone. Typically for men. Derivative of resting bitch face in women.

Girl 1: Why does Bryan look like he's going to kill that kid?

Girl 2: Oh he's ok, he just has resting murder face. He isn't actually angry at all. He's probably pondering football schedules.