Green’s Dictionary of Slang

1. (US) a loafer, idler.

1945		in Yank 20 Apr. 20: You, you goof-off! [HDAS].
1952		K.C. Lamott Stockade 104: I didn’t think those two goof-offs had the guts.
1953		L. Uris Battle Cry (1964) 176: I found my platoon were first-class goof-offs.
1957		(con. 1943) A. Myrer Big War 213: There’s going to be enough groping and sweating around as it is without some goof-off getting blasted all for nothing.
1964		Kerouac letter 22 April in Charters II (1999) 379: I’m an old time French farceur, which is a French word meaning honest goof-off.
1967		(con. 1951) McAleer & Dickson Unit Pride (1981) 3: The others just stood there [...] like a couple of goof-offs.
1973		in C. Browne Body Shop 31: There are so many goof-offs in the army.
1988		D. Poyer Med 231: They were just putting in time [...] they were goof-offs.
2000		Guardian G2 20 Jan. 14: A US site dedicated to ‘slackers, goof-offs, procrastinators, loafers, long lunchers and web-addicted employees world wide’.

2. (US) an error or blunder.

1961		B. Considine Ripley 173: Naturally, a goof-off of such proportions [...] formed the basis of a humorous story.
1979		W. Kienzle Rosary Murders 111: You probably feel bad about yesterday [...] Well, don’t. It was no goof-off. You were doing what you should have been doing.

3. a joker.

1978		S. Longstreet Straw Boss (1979) 271: ‘To all dead friends, good paratroopers all,’ said Mike, lifting his glass. Davey nodded. ‘Cocksmen, goofoffs, pals.’.
1986		S. King It (1987) 570: As a kid he had been a goof-off, a sometimes vulgar, sometimes amusing comedian.