Green’s Dictionary of Slang

five-knuckle shuffle n.

masturbation.

1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: five knuckle shuffle euph. A one-handed work out to a Cindy Crawford exercise video.
2002		Fat Dancer 🌐 Euphemisms Top 10: 10) One off the wrist. 9) Making baldie puke. 8) Jerkin the gherkin. 7) Yanking the doodle. 6) White water wristing. 5) Five finger shuffle.
2004		P. Howard PS, I Scored the Bridesmaids 207: Those five-knuckle shuffles that he’s been enjoying when the lights go out.

In phrases

do the five-knuckle shuffle (v.)

to masturbate.

1987		Eble Campus Sl. Oct. 7: wax the dolphin [...] Also do the five-knuckle shuffle.
2003		Number One Adult Sexual Health Terms Advisor 🌐 Masturbation Slang Male Terms: [...] knuckle shuffle on the ol’ piss pump.