Really, if that's not a reason to stop touching a seat, I don't know what is. Try that sometime when you're on the subway or bus and just see how that action stops immediately. The person might think you're a bit loony but at least you'll have a smoother ride. Go on, practice it now.
I, on the other hand, said this to my 3 year old last night on the plane (our third and last...hmm, child and plane actually). I can't really blame the poor guy for being antsy - we had started our travels early that morning and had been sitting on planes and in airports for about 14 hours so his little legs were, understandably, in need of some movement. But the lady in front probably didn't want to be his exercise equipment so I had to make an immediate and effective threat. It worked. His yellow rubber frog must have been just a tad bit more exciting than the mesmerizing rhythm of the tray table going up and down. You're welcome, lady in seat 24D.