Whenever I see someone with sunglasses inside, I always chalk it up to a) not being arsed to remove them, b) light-sensitivity due to migraine/hangover, or c) being on some sort of drug (sunglasses = invisibility cloak/comfort blanket for some folks).
All of these are totally valid. Douchey is as douchey does, if folks are acting polite/keeping to themselves I don't judge.