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(Sorry, I just had to use that subject line.)
I don't believe there's any insult specific to men that carries quite the sting of "cunt." "Dick" was mentioned above, especially when referring to the Cheney variety, but it's a lower-level insult. Consider: male friends call each other "dick" fairly regularly. I could get called a dick just for, for instance, playing a trick on somebody. Or, if a friend did something vaguely rude, I wouldn't hesitate to say, "Geez, whatta dick!"
In contrast, I have never heard a woman use "cunt" when referring to a friend. As a matter of fact, when a woman refers to an acquaintance as a cunt it is practically a flashing neon sign declaring that said person is, now and forevermore, an ex-friend. As a poster mentioned above, there's a real tinge of betrayal to the word; the word says, "I despise her."
Which, perhaps, is giving it too much power. Nevertheless, I don't think the word is going to be defused any time soon due to usage by America's church-going, self-proclaimed moral-bedrock conservatives.