namely, slag and slut.
I know slag and slut are quite political these days - slut shaming etc. I don't think a woman should be called either of these names just for having a sex life. I am a feminist. But does that mean I can't ever call a woman a name? I'd call him a bastard and that doesn't raise any eyebrows.
Is it a bit justified to use these words about a woman who knowingly becomes the other woman? And yes, it is wrong that there are no male equivalent sexual insults.