It's crazy how something as simple as wearing sunglasses inside can totally change the vibe of your look. Wearing sunglasses when you shouldn't be tells the world that you don't care about the rules. It can also tell the world that you just smoked some weed and you're trying to hide it, but I don't think that's the case with these two. I think they are just a pair of rebels.
The only downside of taking photos with your sunglasses on is that no one can tell where you're looking. When you aren't wearing sunglasses, you can turn your head away from the camera and your eyes will still show where you're looking. That's not the case with sunglasses, so the girl might be looking right at the camera, but it doesn't look that way.