work one's tail off
and work one's buns off; work one's ass off; work one's butt offInf. Fig. to work very hard. (Use caution with butt.) I worked my tail off to get done on time. You spend half your life working your butt off—and for what?
work one's tail off, to
To work very hard. This inelegant locution dates from the first half of the twentieth century. James Farrell used it in Studs Lonigan (1932–35): “This idea of sweating your tail off with work.” It also is put as to work one’s ass or butt off. See also break/bust one's ass.