I vote for the "contagious spirit of fun!" (thks, Sculptor7).
I moved out of the big city a few years ago, but still go back occaisionally. I go for a ride around town whenever I am there visiting the in-laws, and I stop at every stop sign, yeild the right-of-way to every pedestrian on the MUP, and I get nothing but smiles from just about everyone! When I lived in the city I guess I saw myself as more of a 'road warrior,' and the reaction was more mixed.. I was beginning to think maybe my polite behaivior was the cause, but more likely the fact thsat I am relaxed and happy and smiling is what gets a happier response.