dope, idiot, moron, wally, pillock, dunderhead, dimwit

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.

a willy! or a dopey person

Plonker:
Person of Little Or No Knowledge and Electrical Retarded

To be so drunk you're unable to remember the meaning of certain words.

a poo that is so heavy that makes a massive splash with the toilet water that hits your arse and makes you feel wet.

Someone whose words are not worth reading.
See also plonk.