what i have found best and most entertaining, is get a small syringe(no needle) and just  bottled water(if allowed onto plane) and just slurp up a little water and shoot the small stream of water at peoples heads, maybe 2-3 more rows ahead of you. Obviously don't make a funny face, or giggle and such. Keep it cool and see funny reactions.
If that isnt what your looking for, than if your sitting next to a random person, act like you have..
A)Tourettes, pretty over done
B) Schizophrenia, hard to  pull off sometimes..
C) A.d.h.d , while in the middle of a converation
D) Or a terrible coke addiction where you try to sniff everything you can
Just stuff i like to do with friends on a plane.