Green’s Dictionary of Slang

1. to stop doing something.

1861		T. Hughes Tom Brown at Oxford (1880) 97: It’s very plucky of him, but I do think he’s a great fool not to knock it off now till he has passed.
1903		H. Hapgood Autobiog. of a Thief 330: The supply was soon exhausted, and I saw that the only thing to do was to knock it off entirely.
1913		Sporting Times (London) 26 July 1/4: ‘Knock it off and face the music, lad,’ counselled the earnest friend.
1953		R. Chandler Long Good-Bye 149: ‘Look,’ I said. ‘Shove it. Knock it off. They’re no different from anybody else.’.
1968		N. Heard Howard Street 39: ‘Awright now,’ Bill commanded, ‘y’all bitches knock it off.’.
1977		(con. 1960s) D. Goines Black Gangster (1991) 34: ‘Knock it off,’ Prince interrupted.
1984		(con. 1965) W. Terry Bloods (1985) 3: Better knock that shit off, boy.
1993		Tarantino & Avery Pulp Fiction [film script] 26: I’d knock that shit off if I was you.
1994		G. Disher Crosskill [ebook] ‘Knock it off, Napper’.
2005		K. Huff A Steady Rain I i: Will you effing knock it off, Denny!?
2011		D.R. Pollock Devil All the Time 247: ‘Knock it off, Lee. What we do is our own business’.
2015		G. Disher Heat [ebook] [S]he wriggled her slim shoulders. It meant either Knock it off or Maybe later. It didn’t mean Do it again.
2020		C. Hiaasen Squeeze Me 75: ‘Knock it off. Wasn’t I up-front about my hitch in prison?’’.

2. to complete or dispose of something easily or quickly.

1993

I. Welsh Trainspotting 175: The Rent Boy knocks it oaf!

3. see knock off v. (2c)