3. People who think their life is interesting solely because they live in New York
Every week, a new book comes out about a twenty-something discovering love and life in New York. Not just chick-lit. Established authors. Literary authors. For some reason, a huge number of people think that their stories are interesting because it takes place in New York. If you have an interesting story to tell, I would contend that you should be able to tell that story in the most boring of cities (Columbus).
A disclaimer: I have friends who live in New York. They really enjoy it. However, they don't think their anecdotes are special because they live in New York. That's just where they happen to live.
4. People who say, “You really don't have to do this” when you offer to do something nice for them.
This irks me. Obviously I don't have to do you a favor. I know that I'm not in any sort of binding contract mandating me to take you out for lunch or buy you a drink or invite you to join Gmail. I offered. I want to.
When people say that phrase, the majority of the time they really mean, “Thank you—that's really nice of you.” I think people are just really bad at accepting favors (and compliments, for that matter). But if someone offers to, say, buy you lunch to thank you for something you did for them, just accept it and say thank you. Then everyone feels good. If you say “You really don't have to do this,” you put the favor-giver on the defensive. You make them feel like they have to explain why they want to do the favor. Don't put them in that position. Just thank them, unless you really don't want them to do the favor, and then politely—but firmly—decline.