I love to stare down people with sunglasses on. For most, you can determine if eye contact is made when they turn their head or look down. They know if eye contact is made but you don't.
I remember wearing contacts the first time and someone saying - "You'll no longer be able to hide behind your glasses". I discovered this was true - I was using glasses to avoid eye contact.
Eye contact is a measure of where your attention lies. As I watched the pedestrians in NYC there were few who would make eye contact. Making eye contact with a complete stranger is avoided. As I get older, I try more and more to engage each individual I see with eye contact.
"You can't hide your lyin eyes" - Eagles