The word: Paskudnyak
Pronunciation: rhymes with pass could we yak
Definition: A paskudnyak is a vile, rotten, nasty person. The adjectival form (rarely heard, in my experience with Yinglish) is "paskudne".
Origin: Paskudnyak is Yiddish, and earlier from Polish and Ukranian (Yiddish started as mostly German but amalgamated words from lots of languages).
Notes: It is difficult to distinguish this word from other terms of contempt such as schmuck or putz. Paskudnyak is, at least, not vulgar. Looking through Rosten's Joys of Yiddish, I think that paskudnyak is more like "sleazy", "mean" and "disgusting"; schmuck is more fully evil, and putz is more idiotic. Both putz and shmuck are obscene. Also, paskudnyak is much less known, which can be good.
Source: The Joys of Yiddish.