[Butch Cassidy Slept Here]

For future reference if one finds themselves seated next to someone who is spilling over into your seat take the following steps. Politely excuse yourself and get up and head towards the rear of the airplane. (Feign needing to use the lav or a glass of water for a motion sickness pill.) Politely ask the flight attendant in the rear galley to summon a gate agent. If they refuse, tell him or her the situation and ask again to see a gate agent about the issue. If they refuse to call an agent then ask if you could go back up the jetway to speak with one. If all else fails then demand to speak with the captain or first officer.

Depending on the airline this may be good advice. However, I'd like to see what would happen to the person voicing this type of concern if the airline was American or United.