For those not of the 'live and let live' attitude to inconsiderate shorthaul seat recliners, I have witnessed the perfect retaliaton:

THE SNEEZE!!!

If one is looking for an effective way to remind someone that they have just stuffed the back of their head into the space six inches from your nose, there is nothing like a blast of dewdrops onto their pate to make them think a bit more carefully. Works particularly well for baldies! It certainly made the seat shoot back upright here anyway.

For the record, I was a(n) (amused) witness here, not the avenger.