"The street etiquette of avoiding eye contact lets us go about our business without the distraction of interaction."

"Most people wear the New York 'street face.' It’s a kind of neutral expression with a touch of 'don’t mess with me.' It has a do-not-disturb aura. But the truth is that everyone is looking at everyone else all the time. It’s done on the sly, looking away when caught, often with instinctive pretense..."

Most people in New York wear the New York "street face." I do it in New York too and no one ever messed with me (in the 10+ years I lived there). But elsewhere, you can walk along looking happy and friendly. You can make eye contact and when it gets reciprocal eye contact, you can even say "hi," and still, no one messes with you.

Cool animation at the link, by the way...