Great job raising him!

if a guy came up to me and said that I'd take it as a compliment. but I'm a guy too so...

That is not a compliment. That's sexual harassment. Granted, it might be different if he said it to someone he already knew, because some people like that kind of talk. But if he thinks it's okay to speak that way to strangers something is wrong with him.

That escalated quickly

Depends on the situation. Picking up the corner prostitute yes. Buying cookies from the girl scouts no.

If my husband said that to me, he would probably end up sleeping on the couch for a week. If a random man said it to me, they would be singing soprano for a while.

If he says he's Christian Grey then it might be to some twisted mind

At least he didn't try Peanut Butter or Jelly...

this is why father's need to be wingmen for their sons.

It's like a woman walking up to a guy and saying 'I want you on your knees licking my pussy' because when a guy says 'I want to jam my **** in your throat', he doesn't mean: I find you attractive and I want to have sex with you (and make sure you can also ******). No, he says: you should give me satisfaction and I don't care about yours, so the woman is just an object. Women who accept this as a one-liner from a guy they don't know (even if they like to be treated like an object from time to time (nothing wrong with that, but it has to be done on safe grounds)) accept it that the guy just has this awful conviction that he can treat women like objects for his satisfaction when and where he wants it. And that's wrong, because when you try to turn the situation around and treat men like objects, for instance when a strong woman or gay guy makes an approach like this, men don't like this kind of treatment. So women don't have to accept this either. Men and women are not the same but we all should get some basic respect, which means being treated like a human being and not a thing for someone else's satisfaction. So please OP, try to set it right with your son!