Here is an example of the type of conversation, concerning the delightful word 'cunt', that I have frequently observed on feminist websites used by people from the UK and the US.
"US: Cunt is a gendered insult! It is demeaning to women and if you don't stop using it to describe Rush Limbaugh, your feminist card will be revoked!
UK: But for us in the UK, calling someone a 'cunt' is the same as calling them an obnoxious individual, only it's quicker and with added spice. The very fact that we apply it to men as well as to women (like Thatcher, the cunt) illustrates that it is not gendered.
US: Rubbish! You are such an asshole.
UK: So are you. You're also a bit of a cunt, if you don't mind me saying so."
And so it goes on.
Here's how I see it: the word genuinely has different harmonics in the USA and the UK. Because of this, while I avoid using the 'c' word in discussions with Americans, I will happily throw it around when speaking to my fellow Brits.
By contrast, I think 'bitch' is a gendered insult and that it remains so even when applied to men. As far as I can tell (the ever-evolving nuances of language being frightfully hard to keep track of) , 'bitch' is a word that describes an undesirable attribute that is supposedly - stereotypically - female. If you call a woman a bitch, you are saying that she possesses this undesirable attribute. If you call a man a bitch, you are saying that not only is he displaying this undesirable attribute, he is acting like one of those inferior vagina-owning beings as well. Double insult!
I don't see 'cunt' as having the same dynamic in the UK. Here, call a woman a cunt and you are saying she is a vile individual. Same applies if you call a man a cunt. There's no added overtone of 'and, what's worse, dude, you're being like a woman'.
I am slightly hung over from taking very strong sleeping tablets so this may not make a scrap of sense. It is also possible that I have completely misunderstood the concept of a gendered insult. However, I genuinely want to know if I'm missing a chunk of the argument and need to rein in my potty mouth.