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the term plonker started out as a reference to someone who was forever drunk on cheap wine (cheap wine is nicknamed plonk) this person was usualy a homeless person, or poor person.

today the term plonker is a very light hearted insult. Its not even seen as an insult, its like calling someone a wally. Its in no way ment maliciously. you call someone a plonker when they say or do something stupid.
bob - why didnt my food cook ?
john - you never turned on the oven, you plonker.
by Emperor Bubba February 01, 2005
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A British slang term used as an insult meaning idiot. Usually used in an endearing way or when having a joke with someone
Person: you didn’t have to do that you plonker!
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by Alex.tay09 July 12, 2019
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Look at that fucking plonker!
I stuck my big fat plonker up her arse!
by KL June 27, 2003
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