Why can girls do this and guys cannot?

There's double standards everywhere. Why can a guy have sex with multiple girls and be looked at as a champ, and a girl can't have sex once without being called easy or a slut? Why can two girls makeout and it's viewed as hot and when two guys makeout it some sort of disgace? It's just how society is, if I could change things I know I would. If I were you I would have told that girl off.