This derogatory term is a combination of the following words:
1)'(NIM)rod' --which is the
name of one of Green
Day's album and a very good word on its own.
2)'numb(SK)ull' --borrowed the SK and another very good word on its own.
3)'dimw(IT)' --the IT from dimwit--and another very strong and good adjective
and finally, just for emphasis...
4) '(R)etard' --well, enough
said.
Therefore, as opposed to calling someone a
nimrod, numbskull, dimwit, or retard, you can use the oh-so-fantastic word nimskrit!