Someone whose brain is missing. Instead, their skull is full of shit, which they feel the need to spout off at all times.
The guy who offered a terminal cancer patient a life time supply of twinkies is a dumbshit. The guy won't live long anyways, way to remind him.
Having just orgasmed inside your pants, involuntarily.
John said, "Dude, this cheeseburger gave me a pantsgasm."