I grew up in a 3rd world country (now I live in Europe) in a city that by HN comments seems similar to SF (big and full of harmless homeless people/drug addicts everywhere). I remember when I was a kid and I was with my mother I stared to a homeless man for some time. Of course he just seemed peculiar to me, I was a little kid, but this guy got mad and screamed "Do I owe you money or what? why do you keep looking at me?"

My mother grabbed me in her arms and we just went away quickly. She told me to not look at homeless people for so much time. Of course I was very scared, I don't remember exactly how old I was but I still remember the episode some decades later.