I never had much trouble with that even when I was single. However, I happened to be a party to what I thought was the perfect way to handle such a situation: I was walking out of a class, and one of the guys from the class asked one of the girls from the class out. She said, politely, "No. But thank you for asking." There are times in my life I should have told people that I wouldn't have a romantic relationship with them if they were the last man on Earth, and I would have saved myself a lot of heartache.
Then there was the co-worker who decided it was his life's work to relieve me of my v!rginity. I got to use some of my best "drop dead and stay there" lines on him. The idiot would say things like, "You still a v!rgin?" in front of the whole office. (This was way before s3xual harassment became such an issue.) I would usually come up with a scathing put-down, he'd get laughed at by the rest of the office, and that was it. I wasn't worried about him stalking me; he wasn't smart enough. This was the guy who came up with the line, "You believe in the Bible, right? We can be like Adam and Eve!" To which I said, "I don't know about that; I think I'm smart enough not to fall for a line from a snake." Shortly thereafter he got sent to Germany (he was military) and I daresay I wasn't mourning his passing.