I think it's just a certain kind of people who acts that way, and I don't believe those people are worth pursuing. Someday they'll probably realize that the world doesn't revolve around them, and then they may or may not learn the lesson and become better towards others.

It did happen to me once, when I was 20. I was starting to find a guy attractive, and had started to smile at him in hopes that he would notice. When he did notice, he told me "just to make things clear, it looks like you're feeling attracted to me but I have no intention of having any kind of relationship with you". Any positive feelings I may had felt for him disappeared at that moment. Then he proceeded to treat me like trash for a while and - me being who I am - I fought back and we had many long arguments. Then a few years went by when we didn't see each other. The next time I saw him I was at a bar, he walked in, saw me and then walked out. The following time was at university, he seemed to want to talk this time, so I humored him: he told me he was working and having trouble with teamwork (no wonder!). Then I saw him again a few years later and he had become more humble. I made him apologize for the things he did and said to me way back when. Maybe I shouldn't have held a grudge for so long, but I do feel better now. I don't care whether or not I ever see him again, but if I do, we should be able to talk like old classmates without hard feelings interfering.