I downloaded one of those crazy photo modifier apps for my phone. I was at a local watering hole at the time and it was filled with people, so I took a picture of the room and the people in it and proceeded to see what kind of weird effects I could create with the app.
Within a few minutes, I got approached by someone who felt concerned that a photo was taken in their general direction. After explaining what I was doing and making every effort to assuage her fear of having her soul stolen or other such nonsense; to no avail; I invited her to take a long leisurely stroll on a short pier.
Some people think they are due rights that don't exist and going to a public place is exactly where you have no expectation of privacy.