in the eyes of other guys, a man is a pimp if he sleeps with a lot of women. mainly because he has to try and make a real effort to be able to do that. therefore in the eyes of his friends, if he's able to get so many girls, that makes him "cool"
For women, it's considerably easier for her to sleep with a lot of guys... If an attractive girl went up to the average guy and says, "hey, screw my brains out," theres a high percentage that the guy will take the chance. If an attractive(flame suit on for gay jokes) goes up to a girl and says "hey, let me screw your brains out," he's far less likely to get any action.
so guys are pimps and girls are sluts. Not sayin it's right or that I live by that rule, but most people will think that way.
not to mention both sexes support it. a girl will call her best friend a slut if she sleeps around with alot of guys. a guy will call his best friend a pimp or whatever if he sleeps around with alot of girls.
again, not say its right. if you sleep with alot of people, youre a slut whether youre a guy or a girl. but thats just me