I sat next to the fat guy once. Actually, he sat next to me on the last damn open seat after a really long week with a tough client. He was also the chatty type, and made a comment about how he was sorry that I was having to sit next to the big dude.
But since I didn't want to be badgered all flight, I proceeded to tell him that I was happy he sat next time to me in case the plane crashed as I wouldn't have to search far for food. He immediately clamped up and stared straight ahead for the next few hours.