Guys are just way cooler.
JUST KIDDING!!
I am a guy, so I may not have any real insight into this, but it seems to me that women on a subconscious level can't help but compare themselves when they meet or hang out with another woman. Who wants to hang out with someone if they're constantly comparing themselves with them? You'd be self concious all the time. I may be wrong...
Guys? We don't generally think about it that much... unless we're at the gym. And even then, not that much.