Feel the carpet between your toes
Let those dogs breathe. It's a long flight, and you'd like to stretch out your feet and wiggle your toes. No good?
Keep those Chuck T's laced up. No one on this flight wants to smell your foot odor for the next two hours. We get your need to relax, but no shoes/ no shirt/ no seat next to me, thanks very much.
Chat up your neighbor
We've got three hours to kill... tell me about yourself. Airplanes are a great place to meet people, and if you're lucky enough to be seated next to an attractive woman, you're going to try strike up a conversation.
My headphones are on for a reason, now please leave me alone. There are few things worse than spending an entire flight listening to an older gentlemen in the row behind you engage an attractive coed in meaningless banter. Airplanes are 'quiet zones', from First Class to tail fin.