get one's ass in gear
Definition from Wiktionary, the free dictionary
- (US, idiomatic) To exert effective effort; to get going; to get moving; to start producing.
- He had been sitting there for two hours until the boss showed up and told him to get his ass in gear.
- "Ass" frequently acts as a pronoun for self in idioms and expressions as in "get your ass up", "get your ass out of here." The "in gear" references a manual automobile transmission, and the putting of it "into gear" to begin motion.