This is a question we actually know the answer to. If the person sitting next to you on the plane is taking up the entire armrest, they know what they're doing and you shouldn't take it lightly. Our personal advice is to wait for person to sneeze and look up but definitely don't say Bless You. The person will expect the Bless You, despite the armrest incident, but don't go there. Don't be surprised if half the armrest is yours within 3-5 seconds. If you have a better idea, Get us on Twitter with your thoughts and we'll add 500 CrowdRise Impact Points (CIPs) for you.