1. A phrase used to express that something will or will not happen. This expression alludes to the ages-old
superstition that literally knocking on wood would
ward off evil
spirits.
2. To masturbate, said of males.
(made-up scene from GTA San Andreas)
(at the beach)
Kent Paul: (ogling a hot girl come out of the water) Oi
Maccer, just take a look at what just breezed out of the blue. That height, that arse, those jugs, those curves! Blimey if I'd be given the chance now I'd get to chuck my junk in that, knock on wood!
Maccer: Indeed man! Knock on wood, eh. Well alright then! *starts masturbating*
Kent Paul: No,
jack-off Jimmy, not... ohh, *mumbles* fucking Northeners!
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Mark H. Proud Urban Dictionary slang author since February 2004.