The flight was almost empty but as luck would have there was a seat duplicate. A lady passenger told the gentleman in 7D that he was in her seat. He told the lady that there were plenty of open seats - pick one. She wanted HER seat. He refused. Emotions were starting to build as they continued the argument. The Flight Attendant got involved and told her the plane was nearly empty and it was open seating, pick one. To which she refused again. The Flight Attendant then came up to us and we decided to get an agent to sort it out. Finally the agent being told of the problem asked the lady why this seat was so important? The explanation: "I bought trip insurance and in case there is a crash, I have to be in my assigned seat or they won't pay." A passenger seating near the two arguing passengers threw in, "Lady, if there's a crash, nobody will be in their assigned seat!"