 You do these three things on an airplane. You're a d***. Always follow the golden armrest rule. The window gets the window, the aisle gets the outside, and the middle gets both. It's more common than you think, and it's disgusting. Aside from the smell, there are all sorts of germs from bodily fluids, spilled drinks, and whatever's on the bottom of everybody else's shoes that you definitely don't want on your skin. Yes, the clouds are lovely, but if the people around you are trying to sleep, close the window shade. Also, the sun might be coming in at an angle that's blinding to your seat mates, even if it's not affecting you. Basically, don't be a dick.