Katrina: Hey Becky, what happened to you last week?
Becky: Oh I plonked off for a week while I was talking to you. The cops woke me up when the neighbors complained about a foul stench coming from my apartment.
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 neverturned on the oven, you plonker.