break one's ass

1. Exert oneself to the utmost, try extremely hard, as in I've been breaking my ass to finish early. This expression is considered vulgar slang; both ass, for backside or buttocks, and balls, for male genitals, are rude; butt, for buttocks, and chops, for either the mouth or the legs, are informal and emphatic but not quite as offensive. For a more polite synonym, see break one's back. [Slang; first half of 1900s]

2. break someone's ass. Also, bust someone's chops. Thrash or harass someone, as in Jim threatened to break Tim's ass, or The boss broke his workers' chops to improve service. [ Vulgar slang; mid-1900s]