The act of masturbation, when the person shouts the name of a person in the vicinity, and then stares them in the eye when they come to investigate.
Steven is having a "good time" in his bedroom.
Steven: BRUCE WILLIS!
Bruce Willis bursts through the door, stangling a panda.
Bruce Willis: What did you want?
Steven stares him in the eye, awkwardly.
Bruce Willis: DID YOU JUST THUNDERWHACK!!!
Bruce Willis eats Steven's spine.
Penis of moderate length but extreme girth. Often those with thunderchodes chime "girth is more important than length" and take dick pics next to unseemingly wide objects
Guy 1: Dude, I heard Tyler is talking toyour girl.
Guy 2: I'm not worried. I heard his dong is only 6 inches.
Guy 1: Yeah, but hes got a thunderchode. He'll split her in half.