When used man to man "I can't believe you did that, you really are a fucking cunt!" Now the man has not only insulted the other man in the strongest possible term, but he has also called in to question his manhood. A fist fight at this point is very possible.
When used man to man about a woman "Stay away from her, she's a real cunt." Generally a big THANK YOU is in order, along with buying the guy a beer.
Woman to woman, good question. I'm a guy so I can't say, and it is rarely if ever used that way. They don't seem to use the " C " word much.
It has almost replaced the word 'mate', often used in Australia to refer to people in a conversation when they can't be bothered trying to remember your name.
American feminist: I find that insulting
Sick Aussie Cunt: Piss off
Sick Aussie Cunt 1: Sup cunt?
Sick Aussie Cunt 2: Nothing much, cunt.