I take a lot of pictures of people on bicycles. Lots of them. I get all kinds of reactions. There has yet to be a time anyone has really protested, but there is definitely a technique to it. The big trick is to keep people talking and never put the camera down. It also helps, if while I am shooting someone, they actually know what it is I am shooting for. When I asked these ladies if they had heard of a blog called Vélo Vogue they went from hesitant to enthusiastic instantly!
I find if I tell people right off the bat they start to pose. If I leave them dangling for just a moment, I get this kind of fantastic picture. What a couple of cuties! Can't get that driving a Prius.
So if you see me out there with my big, fat camera pointed at you, remember that I am taking a picture of you because you look like a fabulous SF bicyclist (unless you are dancing naked with an Elmo doll, in which case I am shooting pictures of you because there is no choice)!