A few months ago I was alone at an airport, getting my car from the long stay carpark at night. Practically no-one else around. I'm not timid, but when a man then walked past me to his own car, and smiled and said hi, I looked down and didn't engage (and of course my keys had already been between my fingers since I had entered the carpark anyway). We went our separate ways and got our cars, no harm done. My heart was pounding a bit though.
I told this story to DH when I got home, saying that the man had been very thoughtless to do what he did. DH said why shouldn't he be friendly? More people in this world should be friendly. And why on earth were you so rude back?
Adult DD was also there when I told him the story. We both tore a strip off him! I think he was quite shocked, what was blindingly obvious to me and DD had never crossed his mind.