I see. I just remember some of your shots of street life in Macau. I've tried taking more people photos discreetly, but it doesn't always work out as I find it much harder to frame the shot and do what I want that way. If it was at an event, then yeah, I think people expect to be photographed and is generally ok with it. It's just shots randomly on the street that I don't know how to approach. I guess it's good to hear though that no one has gotten mad at you so far.
I was now looking back at my shots from this trip and can understand what you're referring to. There are, indeed, some candid shots.
Thinking about it a bit, I can see two reasons for that:
1) Wide-angle. You see, shooting at 15mm, I can be pointing in a totally different direction and still capture the subject. I use this a lot. I normally even antecipate the shot and I'll be waiting for the subject to be at the place I want in the frame. They will acknowledge me (with the camera already at eye level), but they'll never guess that they're in the frame.
2) For some reason, being in a foreign country (which, normally, is flooded with tourists) makes me a bit more "loose". You know, being a tourist, you can be that silly guy that shoots everything and locals won't give a damn. I probably wouldn't do most of those shots where I live.
(Of course, this can be a false feeling and it can potentially get you in more more trouble than shooting people in your home country, but that's another story...)
There are some candids at 135mm, too. But the reason for those is obvious: I'm far from the subject and the my 135mm is so small it won't raise any eyebrows.