get off one's duff

get off one's duff

Get moving, become active. This slangy idiom uses duff in the sense of buttocks, a usage dating from about 1840 and at that time considered impolite. It no longer is, at least not in America, and if anything this cliché is a euphemism for still ruder synonyms, such as get off one’s butt or get off one’s ass.
See also: duff, get, off