Sometimes on a flight I just want to sit down, put on my MP3 headset, read a book or work on my laptop, and be left alone.

However, when the cart's coming, I feel it would be impolite to just ignore the FA and waste their time trying to get my attention, so I stop what I'm doing until I can make eye contact and wave them off.

I wish there was some way (at least in F) to indicate "Do not disturb" (I have contemplated stealing a door hanger from a hotel and hanging it on my ear. I suspect this would not go over well)