It could be pitch black out during the dead of the night when there is not a ray of light around and “That Guy” would still cling to his sunglasses more than Roddy Piper in They Live.
He didn’t just come from the eye doctor after getting drops put in, he isn’t Stevie Wonder or Ray Charles, and he certainly isn’t a celebrity with the paparazzi chasing him for pictures. He will most likely be a hipster with a pair of ironic sunglasses, a preppy with aviators, or a guido with a pair of Dior or Louie Vuitton oversized sunglasses glasses.
Apparently only “That Guy” and Corey Hart* wear their sunglasses at night.
* I wear my sunglasses at night
So I can, so I can
Watch you weave
Then breathe your story lines
And I wear my sunglasses at night
So I can, so I can
Keep track of the visions in my eyes.
- That sounds about right for “That Guy.”

I think I’ve seen that guy in the mall a few times too.
The only reason I could possibly think of for doing that is so that they can check out the bodies of females around them without them noticing. Wearing sunglasses, though, I doubt they’d have any hope of scoring.
I’ve seen these guys. The first thing I think is they’re high.
[...] glasses. If not glasses, he will often be wearing a pair of oversized brightly colored plastic sunglasses at nighttime. Just like his haircut, if he can grow facial hair, it will most likely be something “ironic” [...]
In the words of Larry David,”only two kinds of people wear sunglasses at night or inside, A@#holes and blind people!”.