why is it acceptable to call men and women whores, and sluts?? but when a man is called a slut but when a woman is a whore its a horrible thing and is looked down on????

something that was sent to me via a facebook message made me think about this today. from someone that didn't i know whatsoever sent me facebook message calling me a whore. so why is it okay for a man to say that he's a whore and laugh about it and be joke/badge of honor, and something to brag about. but when a woman is called a whore. it's completely on how she's viewed by everyone as she is a dirty girl, has sex with man after man, she's this horrible person, and that you should stay away from her etc., why should it be completely two different stories when a man is called a slut V.S. a woman being called the same thing? because you don't know what is going on in someones life or the things that they're dealing with? so why is it ok for you to judge some one that you don't know?  why in today's day and age is socially acceptable when it absolutely shouldn't be?