I was wondering your views on this..if a woman sleeps with alot?

i was watching my show 2 and a half men.they make alot of jokes on that show about ..well it made me want to ask this ?.why is it that if a woman sleeps with alot of men she is considered a tramp or loose,but if a man slept with the exact amount of women he would be cosidered a stud..why is that?what is the difference,i don't see one myself