it's called keeping your legs shut Cecile you ignorant slut
You'll have to convince these people they don't have a right to have sex without consequences.
Overheard a young twentysomething woman toss off this line to her friend: "He asked me if I wanted to sleep over, I said No" and offered some reason she was busy that night -- but implied some other night might be fine. It's an aggressively casual attitude towards sex, isn't it.