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rude slang A jerk. This phrase plays on another expression, "have (one's) head up (one's) ass," which means to act in a way that others deem stupid or obnoxious. This phrase evokes the image of someone using their buttocks as a hat. Quit being an asshat and help me with this! Ugh, that guy is such an asshat—don't even bother talking to him.
1. n. the imaginary garment worn by one with one’s head up one’s ass. (Offensive.)
2. n. a person said to be wearing an asshat (sense 1). Wake up you stupid asshat!