Sacred advice. Nice. Thanks, I like that. Even if it's not true. I'm no saint, so it's more like damned advice. So here's my damned advice on your question...

For starters, I can't tell you how not to turn your guy off because I don't know how he will react to anything you say. Nor do you. People are unpredictable. You can't worry about how your guy will react. He will react how he reacts. If you want the behavior to stop, all you can do is be honest and kind. You hope that your actions and words are taken as they are meant, but if not, that's his problem, not yours. His reaction is out of your control.

So there's that.

The least aggressive response to his lewdness is silence. After three or four of his dirty remarks are met with awkward silence from you, he should get the hint. Whether you guys are flirting in person or online -- you didn't say -- just don't reply. He says those things to get a reaction from you, so don't reward the behavior by giving him one. Silence can say much more than words sometimes.

If that doesn't work, then you'll just have to be blunt, and that's fine as long as you do it with kindness. Tell him that you enjoy talking to him, but you would prefer he not make off-color comments. If he asks why, you can tell him that the comments offend you. If he gets annoyed, so be it. You were honest and polite, and that's all you can do. If he can't handle it, he's likely too immature for you, anyway.

There's your damned answer. I hope it helps.