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general::
Phrase(s): work one’s tail off [and] work one’s buns off; work one’s ass off; work one’s butt off
Inf. 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?
McGrawhill's American Idioms And Phrasal Verbs