I am one of those people who jump easily. You can tell me you are going to scare me and I will still jump when you say, "Boo!".
Now, realize I live in a city where every taxi driver that passes honks at you, at least once, just to be sure you realize they are there and willing to let you be their next passenger.
Ya, I jump quite often as I walk down the street. I am sure it amuses those walking behind me.