nimskrit
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!

One of your 'nimskrit' sisters left their flip-flops in my car. I'm guessing it was Melanie since it was directly behind my car seat.