Is there no word in the English language that is as negative a label for somebody as the slang for a vagina?
Probably should note I was paraphrasing from the cunt rant in "In Bruges. " In British usage, the word is more akin to "jerk" and not as offensive (or vaginal) as it is in the US.
Many of the alternatives, like cocksucker and prick and dick, are also referencing something about sexuality, so that just leaves asshole (everyone's got one of those) or shithead (and other scat variations). I will edit the post, as an experiment in invective, with one of those other terms and we can see how that works.