Just a fem rant

Hey- feel free to pass this up if feminism stuff isn't your thing. 
I'm a teacher assistant in an oceanography class, the class is loads of fun to TA for but some of the students. There's a group of guys that're republican and call themselves "meninists" or whatever. (Nothing against all republicans but these guys truly make reps look REALLY bad, sorry you've got those num nuts)
Anyways, one of them is aware that I am a feminist, women are all technically feminists after all, and he looks at me and says "feminism is the dumbest thing. Why do we even need it. It just tells girls it's okay to be sluts" (AHRHFJ THAT WORD)
And I told him off about the usage of 'slut' and told him that feminists try to empower women, and that they're not telling girls to sleep around, but are trying to teach them that there is no shame in what they choose to do with their sex life. 
The guy didn't get it. I asked him why it's okay for men to sleep around and he said "it's expected of us. We're supposed to do that"
Like...that's exactly one of the things that I believe feminists are thing to stop. Is the thinking that guys have to do this and that of girls need to do all these things and none of those. 
Ugh it irks me is all. 
And yes I know that's not all feminism is about, it's just this particular thing I'm talking about. 
Opinions are welcome of course on what you think about all this stuff.