Almost certainly originates from a TV coffee advert of the 70s/80s starring Gareth Hunt. He holds several coffee beans in a half-clenched fist then shakes them in a way reminiscent of a hand job. The relationship with Gareth Hunt is further strengthened since he was a considered to be a bit of a wanker.
Euphemistically used to replace wanking or a hand job. Imagine holding a cup of Nescafé in your hand. If your imagination can't stretch to Nescafé, Aldi value granules will suffice. Then imagine shaking someone's hand with it. Then see what you've just done in reality. You see.
The whore gave Hugh the old Nescafé Handshake before selling her story to the classy upmarket newspaper 'The Sun'.
British slang term to describe (in past tense) an insult by using the hand in a tossing/jacking off motion.
Nescafe (pronounced Nes-caf-a) is a coffee, who's ad on TV used a man (Gareth Hunt) that shook coffee beans in one hand like he was masterbating (very funny)
You are driving your car and someone cuts in front of you sharply. Lean out of the window, extend your arm and yell 'wanker!' while curling your hand and moving in a fast wanking/jacking off motion.
You have just performed 'The Nescafe Bean Shaker'!!
Ben "I was driving this morning and some prick cut me up!"
Bill "What did you do?"
Ben "I give it the old Nescafe bean shaker out the window"
Bill "No really?! ha ha"