Stop the person in front of me from reclining their seat on an airplane?

You cannot stop the person in front of you from reclining their seat. Arrive at the airport early and try to get an emergency row window seat (the other seats in front of an emergency row DO recline, but not the ones by the window. Even with the ones in front of you that do recline, there's still more room in the exit row). Or, you could also try to get a bulkhead seat (right behind first class or business with only a wall in front of you, so no one to tilt back). You could also consider purchasing an upgrade at the airport. If you use the self check-in machine, and there's availability, when you go to check in, it'll ask you if you'd like to purchase the upgrade for $XX amount of dollars (depends on distance you're traveling,etc.) In First Class, even if the person in front of you tilts back, there's still plenty of room for you.