When tapping on the seat back screen, I usually use my hand to hold the seat in front of me then use my thumb to tap it lightly. This minimizes seat vibration.
As for how to deal with it, politely thank that person for the head massage with a smile, then ask that person if s/he wants to take a break. The bottom line is, most of the people are not bad person, they just don't realize the inconvenience they create.
On a side note: there is game on the narrow body IFE? I know the newer system has Sudoku and Chess and some other stuff. I have no idea the old system has them too.