break/bust one's ass

break/bust one's ass

Exert oneself to the utmost degree; work very hard. This rather vulgar usage dates from the first half of the 1900s. Norman Mailer had it in his war novel, The Naked and the Dead (1948): “What’re we breakin’ our asses for? Let’s take it easy.” Sometimes “butt” is substituted for “ass.” See also work one's tail off.
See also: ass, break, bust