I first heard the word 'plonker' back in 1964, when I was a 17-year-old engineering apprentice, and a tradesman I was 'the lad' for was berating his other charge for spending too much time in the toilets. The accusation was hurled that the apprentice was constantly 'running off to the bogs to pull your plonker', in other words masturbate.

From that moment, 'plonker' was firmly set in my mind, and has been ever since, as a euphemism for 'penis'.