Green’s Dictionary of Slang

1. to have sexual intercourse.

1980		E. Folb Runnin’ Down Some Lines 244: knock it out Engage in sexual intercourse.
1997		Solar Project ‘Zeitgest’ 🎵 on ...in Time [album] We honk for cookies, we knock it out / We mash the fat, we mess around / Jig-a-jig, rub-a-dub, dead shot, Donald Duck / You wanna feel my Bethlehem steel / Mary Poppins, TNT, Bristol City / I bite into your cats and kitties.

2. to do anything quickly, with neither style nor concentration.

1943		R. Llewellyn None But the Lonely Heart 271: All the joannas knocking it out.
1964		D. Gregory Nigger 55: Before they could get going, I'd knock it out first, fast, knock out those jokes so they wouldn't have time to set and climb all over me.
1978		R. Charles Brother Ray 141: I had the kind of band which could knock out a good riff once it was set for them.
2005		B. Coleman Rakim Told Me 45: ‘[W]ith the group, it was boom-boom-boom, knock the tracks out’.
2007		B. Coleman Check the Technique 19: ‘When you’re in a commercial studio, you just have to think a different way, like: “Let’s knock this song out and get out of here’ .

3. to spend money.

1955		B. Hill Boss of Britain’s Underworld 29: Most young burglars make the mistake of having a tickle off and then knocking it out on women, speilers [sic] and drink.
1961		(con. 1920s) J. Sparks Burglar to the Nobility 24: Of course we were knocking it out in the clubs and spielers nearly as fast as we got it.