I take pictures of strangers all the time, as part of my job...passengers getting on or off buses and trolleys, people waiting at bus stops or sitting in the station lobby. Most of the time, people are either oblivious to it, okay with it, or (very, very often) they give me a look and then quickly leave the area where I'm shooting.
I've had people come up and request that I NOT take the pictures, I've had a couple come up and ASK me to take their pictures...I've had a new bus operator call security on me because I was "suspicious" lol, and I had one guy come up and say "I don't know what you're doing, but you can't take my picture because I am a legal, law-abiding citizen who is not doing anything wrong." Seriously! So, of course, at the first opportunity, I took his picture anyway...
I did miss a GREAT shot a couple of weeks ago, because I'd already put my camera away when a guy came walking across the bus platform (which isn't allowed) carrying a guitar and a CHAIR...like a wooden dining chair...he couldn't understand why they weren't going to let him on the bus with that chair!
Most people who even SEE you taking their picture will either ask you to stop, start posing, or they will simply walk away. Having a "reason" you are taking photos of them is always helpful--I have the built-in excuse of it being my job, but you can always say "I'm working on a project," or something like that. You don't have to mention it's your own personal project!
One note: I also recently went to one of the local corn mazes and shot photos of unknown adorable children. I suspect that I got away with this because I am a female...I wouldn't really suggest males chase around after young children they don't know, taking their pictures, or you'll probably end up explaining yourself to the authorities. It's unfortunate that people would be suspicious of a male doing that, but not a female, but that seems to be the case...at least where I am.