I can't believe that somebody would do something nice for me. Whenever somebody does or says something nice to me one of two thoughts go through my head. "Why? What do you want from me? Who put you up to this?" or "Oh no. You have me mistaken for somebody who isn't a loser/asshole." Likewise, whenever I hear somebody say negative things about an unnamed person I immediately assume they are talking about me. Even here, in EC, which is possibly the nicest community I've ever been a part of, I feel these things.
I'm very familiar with this mindset. I think it all boils down to self-esteem, really. You think of yourself as a "loser/asshole" who isn't worthy of random acts of kindness, and is even the target of every bit of audible gossip. What worked in getting rid of it for me is a philosophy of live and let live. I've also seen it categorized in terms of "OK-ness" with an attitude of "I'm OK; you're OK." You are confident in your self-worth, and because of that, you allow other people to do their thing without casting suspicion on them. You wouldn't believe how much stress evaporates instantly once you start thinking like this. I'm OK, You're OK - Wikipedia, the free encyclopedia