I love taking photographs of people Including strangers. Especially strangers. Strangers, however, don't often reciprocate the feeling. In fact, I think it's pretty safe to say that most people do not like some random person taking photos of them.
But I do it anyway. In a secretive, furtive fashion, I quickly point my camera at an unsuspecting person, snap, and just as quickly, point my camera at something else, as if to say "nooo... I wasn't just taking a photo of you, I was taking a photo of this lovely wall or rock or pole or whatever..." As if they believe me. But I try. The problem with this approach is that you don't always get the photo you want, but sometimes you get lucky.
It also helps if they never notice you in the first place (zoom lens around a corner, although that's kind of creepy) or if you look just like some dumb tourist, like I did in Portugal, where I took these shots.