Masturbation: The phrase comes from the act of masturbating using the whole hand, wrapping 4 fingers round the shaft of the penis, and the thumb round the other side, hence "five knuckles".
Geordie 1: Howaye man. Did ye score last night?
Geordie 2: Ney chance. I was gannin' the Five knuckle shuffle till it felt like me hand'd fall off.
Another word for the popular slang word 'wank'.
Most commonly used in pub-talks between men of age 18-30 to describe masturbation in a funny way, normally about someone, rather than themselves.