Civilized Air Travel does not include smearing up the back of your seat

Speaking of things not to do if there's someone sitting behind you...

Some lady on the plane back from Cuba

Let me turn your attention to air travel, specifically civilized air travel. One rule of etiquette might be:

Do not rub your fingers all over the screen on the back of your seat.

I don't understand the contortions necessary for this sort of rear overhead relaxation. I envision the armpit in the stewardess's face though. "And ma'am, what would you like to drink..." cough cough cough.

I showed the above photo to someone and they said I should have leaned forward and licked her thumb. I would have considered this course of action had it not sounded so truly unhygienic.