i think the most offensive insults are the one's that hold a piece of truth to them. so...to an overweight person "b****" wouldn't be as bad as "fat ass." edit: man there are sure a lot of c*cks*ckers here.
what about b*tch? not only are you dehumanized and compared to a dog, but you also suddenly underwent a sex change... i don't know, i curse a lot and use rape way too much....so i can't say any of these are too insulting...altho buttmunch would probably stun me speechless cuz that's so 6th grade...
I think c*nt wins just because it hasn't been overused. It still carries all of its raw, emotional impact. B!tch is a minor personality trait (or in some women, a regularly occurring temporary personality trait), whereas I would reserve c*nt for a woman who totally f*cked me or a friend over. As a matter of fact, it's such a strong insult that I have never had cause to use it.