[AndyShields]

If you look at someone like Jen she's become hated for being bitchy, but Luke's still relatively popular despite being so much nastier and bitchier.
Look at the 'Whisper Club'. Sylvia and Jen went out to choruses of boos while Dale and Stu had huge cheers, both were nastier and more aggressive and involved in Spitnight than the women but their part gets forgotten.
I think it's more to do with stereotypes than anything else.
We're used to the stereotype of bitchy girl, but there isn't really a common bitchy guy in the media (Except the bitchy gay stereotype) so when a guy is insulting someone behind their back it isn't really seen as bitching... Whereas because we're used to seeing the stereotypical bitchy/slutty girl they're more likely to be identified as such.