Dictionary — ontologydriven

knock boots en · VERB

Perhaps from the notion that boots placed beneath one's bed knock one another due to the shaking of the bed during sex.

(euphemistic, slang) To have sexual intercourse, especially recreationally if not casually.
- You ain't knocking boots/ You ain't treating me like no prostitute 1986, “Tramp”, in Hot, Cool & Vicious, performed by Salt-n-Pepa:
- After we done, bill a spliff and cotch / Pour me a glass of the Henny on the rocks / And get ready for round two / Cause any time we knock boots you know we knock twice 2016 February 14, Joseph Adenuga, Darren Dixon, Tariq Devega, “Ladies Hit Squad” (track 6), in Konnichiwa, performed by Skepta ft. D Double E and ASAP Nast, Boy Better Know:
- Of course they fall madly and deeply in love, as Biker Dude learns to respect a girl who won't knock boots on the first date. 1994, Marshall Crenshaw, Hollywood Rock, HarperPerennial, published 1994, →ISBN, page 250:

Spelling	Features	Source
knocks boots	Number=Sing, Person=3, Tense=Pres	lexicographic
knocking boots	Tense=Pres, VerbForm=Part	lexicographic
knocked boots	Tense=Past, VerbForm=Part	lexicographic
knocked boots	Tense=Past	lexicographic