A Dumb Ass was a derogatory term used on Earth in the 20th century that was used to describe a stupid and obstinate person.

After traveling back in time to the 20th century with the crew of the late USS Enterprise, Admiral James T. Kirk had stepped out in front of a cab, which was barely able to stop in time to avoid running over the Admiral. The driver of the cab angrily demanded why Kirk didn't watch where he was going, and then called him a dumb ass. Momentarily at a loss for words, Kirk responded by calling the driver a double dumb ass. (TOS novelization: Star Trek IV: The Voyage Home).