If eyes are the windows of the soul, what are sunglasses? They are for hiding. People don’t want to be watched all the time. They want to choose when to be on show.
Carrying on the blog about people whose faces are in shadow, you really want to see their eyes.
If someone’s wearing sunglasses when you’re talking to them, ask them to take them off!
Otherwise mirrored ones are handy for girls to repair lip-gloss. Guys can smile ironically depending on whether the person is bigger than you. A wild change of subject works, e.g.
“Do you like pistachio ice-cream?”
The sunglasses will come off to show you their raised eyebrows! Follow up very quickly by positioning yourself to see them brilliantly and comment on their great eyes! Then it’s much easier to continue the conversation.