Green’s Dictionary of Slang

kaycuff v.

[backsl. ]

used in senses of fuck v.

[Aus]Sydney Sportsman (Surry Hills, NSW) 24 Oct. 1/2: The next meeting it [i.e. a racehorse] had a lash and got kay-cuffed, and no one felt a bit sorry for the crowd].
[Aus]R.G. Barrett Davo’s Little Something 13: They could say things in front of customers and the customers would be none the wiser [...] ‘Dratsab, teenuck, teg kaycuffed,’ etc, etc.
[US]J. Burkardt ‘Back Sl.’ Wordplay 🌐 kaycuff foe: fuck off.