For the love of God, please read and heed. Let's all get better at flying together.
  1. Paint your fingernails - Have you no consideration? You're choking everyone out. I'm not even sure that's legal. Related: Try like hell not to bring McDonald's food on the plane. That smells bad too.
  2. Talk to someone who isn't interested in talking - Have some situational awareness. Not everyone wants to be chatted up. Sometimes people would prefer to be left alone. A good indicator of this is when someone is wearing headphones which are not plugged into anything.
  3. Linger/loiter next to someone's seat for an hour - Older white men usually commit this offense for some reason. Dude, sit down. We're all cramped. Don't you understand that your junk is eye-level and that's invasive?
  4. Neglect to bathe - Don't get on an airplane smelling like you just ran a marathon through a landfill. I don't care where you're from or what your culture dictates; flying commercially means you'll be in close quarters with others and the sour stench of body odor is a pain no one deserves to endure for hours.
  5. Completely lose yourself in the in-flight entertainment - I once sat next to a man who was so engrossed in the on-demand video that he forgot there were people two inches to his right and left. In his mind, he was at home on the couch. He was biting his fingernails off and dropping them in a nice little pile on the leg of his sweatpants. Gross.