However, I do recognize that there may be some good reasons for wearing sunglasses indoors. Something else sunglasses do is obscure your face, making you harder to be recognized. Thus, they can be very useful to people such as celebrities and criminals. Celebrities, because they don't want to be mobbed by fans everywhere they go. Criminals, because they don't want to get caught and turned in.
But what about when people who are neither of these wear sunglasses indoors? What's the point? Is this some attempt at looking cool? At remaining aloof and disinterested in the affairs of people so unimportant they don't even deserve eye contact? Or is this a way for you to check out girls without them knowing it? I'm going with all of the above. Therefore, the only explanation I have is that these people are tools. Well here's some advice pal: if you want to look good or tough, hit the gym and lose weight. That'll do a lot more for you than those sunglasses.
(One notable exception to this rule is the people in the Matrix. Everyone seems to like wearing sunglasses there, regardless of where they are in the matrix. There's probably some deeper meaning behind this (the movies are quite deep, actually), of which I am not aware. So I'll refrain from holding the matrix people to the same standard...for now.)