When you are nice to a guy it can sometimes awaken his sexual desires for you.  In other words a woman is willing to do such a nice thing for me, maybe she might do more nicer things for me.  It also makes him think he can get away with doing things he might not of considered doing, because if you did that nice thing for him, you would more than like put up with him having some fun and talking dirty.

Talking dirty should not really be done too early by a guy, because ultimately you need to get to know the real him first before he talks dirty.  Unfortunately immature men and over-confident men, both try to get to talking dirty as soon as possible.

The problem is men get bored by general chit-chat, like what are you doing at the weekend, he has the same boring conversation with other men and women all the time.  Talking dirty is exciting and fun to a guy, they don't realise that women might not feel the same way.  In fact I don't think you can label all women as hating dirty talk, nor can you say that women enjoy dirty talk until they know the man a lot.  So it's up to a man to work out whether a woman likes dirty talk or not.

The problem guys have, is that they are taught, any woman that sees a guy as nice, is classed as a friend.  Therefore men feel as though they need to bring sex into the conversation as soon as possible in order to stop a woman thinking of him as a friend and make her imagine him having sex with her.  They don't realise that they will be classed as dirty men or perverts because ultimately other men get away with it and win women over, so why can't they.

Talking about sex is fun, it can be almost as much fun as actually having sex.  Yes, most guys want to get down to having sex as soon as possible, but talking about it, maybe helps delay it in a way, because having fun talking about it, means he can get some thrills and anticipate and imagine having sex with you.

Another element of it, is a guy could be testing how much you like sex, how shy you are, how comfortable you are discussing things.  After all, if you are comfortable discussing sex, then you will more than likely be comfortable discussing anything else with him in a calm mature way.

So there's a lot more complex things going on when a guy talks dirty to a woman, I don't think guys consciously know themselves how complex the things are.

Really though out of politeness a guy shouldn't really be talking dirty from an early stage, if he is, then he's immature or thinks that's what women like, or else he's not too bothered about a relationship with you so he decides to take the risk and if he frightens you off, he won't lose sleep over it.

I personally, make some brief sexual comments as early on as possible, see her reaction to them, but ensure that the sexual comments are in context with the fact that I'm not going to use the woman for sex and that I don't constantly talk about sex night and day, I can talk about sensible subjects as well.

Men don't really get any enjoyment or stimulation from talking about emotional things, they get excitement from talking about controversial subjects and sex.   And essentially they talk and listen to you talk about emotional things in order to satisfy your needs and hope that you will talk about something that they find interesting, which is often sex or something controversial.   It's stimulation, but it always makes him think this girl is interesting she can talk about a wide range of subjects including sex and not be uncomfortable with it and that bodes well for the long term relationship.

You've got to realise that men and women are different, women don't like some of men's differences and equally men don't like some of women's differences.  For women and men to get on well, it's important that both compromise and put up with some of those differences, of course that all depends on whether their positives outweigh their negatives.

Talking about sex is fun and I bet you if you found a guy that you are really attracted to, if he talked dirty to you, then you'd love it.  But the fact that you are uncomfortable with these other guys talking dirty to you, is because really you haven't had a chance to become attracted to them or get to know them yet or you don't really find them attractive.  That's a guys struggle, does he not talk dirty and seem like some boring nice bloke or friend, or does he risk talking dirty and either end up being a perv or being someone you see as a stud.

So I guess what I'm saying after all that, is men should be able to express themselves, as long as they are sensitive to a woman's feelings and express themselves at the right time, when a woman is comfortable with talking about that sort of thing.  Clearly the guys you are talking about are doing it far too early.