"Act as if you are making a video. Hold the camera high and walk slowly as if you are recording, while actually taking photos whenever something interesting comes along. People seem to care less in that case as they are not your main focus - a video usually means that there's no single subject but you are rather capturing the vibe of the city. You can even act like you are a tourist exploring a new place. Using LCD screen instead of viewfinder also helps to seem less like a professional."
This is all some great advice. I particularly like this one. What you say here is so true!
Yep, the more you blend in and appear goofy, the less attention from people. Of course, the best is when you are completely relaxed and don't have to pretend at all.