Interestingly, spectacular looks in the animal kingdom are more often than not strictly a men's department thing. Watch a feature on virtually any animal on NGC or Discovery. Females need to be impressed, the males are impressive. Now we come to good old Homo Sapiens. A species that certainly goes against the evolutionary grain.
Females are the divine objects of beauty, males tend to be on the receiving end of the whole affair.
But of course it's not that simple. Being the complicated creatures we are, there's a twist. Yeah, that's it. Nothing as base and animalistic as biological urges here. We want to look good because it's a statement of how much we respect ourselves and how deeply we feel as one with our bodies.