work one’s butt off

work (one's) butt off

To work really hard (on or at something). I know you thought it was just a silly New Year's resolution, but I've been working my butt off at the gym! Sally and Jim work their butts off when we hold our consumer conference each year. I don't know what I'd do without them!
See also: butt, off, work

work one’s butt off

verb
See also: butt, off, work