Don't recline the seat.
It's rude and the person behind you almost certainly wants you dead.
We all have very little personal space on a plane, and reclining just takes valuable breathing room from the person behind you.
And don't use the old "I'm sleeping" excuse. The seat reclines two inches. Is two inches really the only thing between you and a nap? It's called common courtesy.
I can't speak for anyone else but when someone reclines in front of me I'm imagining every possible way to annoy them for the rest of the flight.