This problem sounds very familiar...At the start of the school year, I was making all sorts of friends, getting to know lots of people, having conversations with them, etc. I thought that all these people must really like me.
Then, I would be at lunch, sitting alone, and catch their eye, but they would go sit with someone else anyways. Or I would walk past them and they wouldn't even so much as look up at me or say hello. Or I would be at some party or other event and see them there but they wouldn't bother to come over to talk to me. So, I reached the conclusion that no one liked me, after all.
Until I realized something. When I'm at lunch, I don't always have the guts to walk up to someone and ask if I can eat with them. When I'm walking to class, I'm not always looking at the people around me. And even when I see someone that I know, I'm often too shy to just walk up and talk to them, at east if that person is a girl. But when I do this, it's just because I'm too shy or not paying attention, not because I have anything against that person.
Anyways, once I realized this, I saw that maybe other people were just shy too, maybe just like me, they sometimes did something that made them look like they were avoiding me without really meaning to. So now, I'm giving people the benefit of the doubt, and trying to reach out to them whether or not they have done so in the past. Maybe there are some people who really were trying to avoid me, and if so I'm probably annoying them, but it's better than losing a friend because I was insecure and imagined that they didn't like me when they really did.
(And I think I already completely wrecked a friendship with one girl because I managed to convince myself that she didn't like me and that the best thing I could do was "give her some distance" before I realized that. Sigh... I'll give it another shot when I get back to school.)
I know what you mean about even people you don't really know (like waiters and cashiers) seeming to dislike you, but I can say from experience that a lot of this comes simply because you walk around with some sort of subconscious assumption that there's "something wrong with you" and that people are purposefully avoiding you.
