Why would someone wear dark sunglasses in a dimly lit bar?

I was recently in a bar/grill at the behest of a friend of mine. I had not been in such a place in ages. There was good food, a band, and a couple of people dancing. Things were very upbeat and nice even though it was poorly lit and a little too dark to read the menu. At the bar there was a guy wearing dark sunglasses.
Why? Maybe it’s the way my mind works but I could only come up with negative reasons: hiding bloodshot eyes, hoping to not be recognized, trying to look like a rock star on stage, etc.
Why would anyone wear dark sunglasses in a dark bar? Do you?