I understand what you're getting at, but the way it's phrased annoys me.
Believe it or not, men like sex. If they're horny (usually), they'll pursue sex. They'll talk about sex. They'll want sex. That's what happens. If he's messaging you on the internet and you don't want to discuss sex, tell him so. If he persists, block him. In face to face interactions, tell him you don't want casual sex. If he doesn't like that, leave, and seek legal action if he starts harassing you about it. That's all there is to it. There's nothing wrong with propositioning you for sex, and there's nothing wrong with wanting to discuss sex with you. If men had lower sex drives than women, the women would completely hate it (look at the questions on this site from girls talking about how they want their man to be more interested in sex, and you'll see what I mean).
If you don't want to have or discuss sex, then say so. That's all there is to it. There are men and women who want relationships, and there are men and women who just want casual sex. Neither one has "good" intentions or "bad" intentions, just different views and goals. There are plenty of men out there who prefer relationships to hookups- if you really want a guy, go out and find him.