Since when is sleeping around not a slut/man whore?

My new friend (let's call her Syd) told me straight up that my now ex best friend (let's call her Anna) is a skanky slut. This was before our friendship messed up. I was shocked and a little offended when she said that. I was like, "What? Don't say that!!" Syd said, "Well it's true! Anna pushes guys to have sex, sleeps with them. It's true and you know it! You just don't wanna see that."
I didn't want to believe Anna was a slut.
Some user said it doesn't make her slut and it makes us two ladies bitches for calling her that.