And, sometimes, folks, it is civilized and rational.

Me in 27D, MrQ in 27F, empty seat between us.

Other passenger: "Sir, I think you are in my seat. I have 27F."

MrQ: "Oh, let me look at my boarding pass. You are right, I'm in 28F. I guess I just assumed I was in the same row as my wife. I'll move right away."

Other passenger: "No problem. I'll just take your seat. You can stay with your wife."

MrQ: "Thanks. That works for me."

Me: "That's very nice of you, thanks."

Imagine that. No screaming, no hysterics, no drama. Just a nice, normal interaction between civilized adults.