Can I have your seat?

I have spent a lot of time in the air this year. And I really dislike being on an airplane for long periods of time. So, I carefully plan out flights, especially ones on which I won't get an upgrade. For the routes I take regularly, I know which seats and rows are better than others and request those seats. Twice already this year, I have gotten on the plane and found people assuming that they can have my seat.

On a recent trip out of LAX, I was in a pretty dark mood. After sitting in traffic for two hours driving to the airport from the valley and then spending 30 minutes in line at the security checkpoint, I was just ready to kick back and get the heck out of Dodge. I get on the plane with about 20 minutes left before departure and there is someone sitting in my seat. A couple that had gotten booked on the plane at the last minute could not get seats together. (The plane was completely packed.) So, "her" seat was a middle seat in the center of the plane.

When I said, "Excuse me, you are in my seat", her husband responded that they could not sit together so they figured I would not mind taking her seat (in the middle). I was fairly taken aback by this and said, well, yes I do. While the wife was moving back, the guy made a point of making sure that the flight attendants and everyone in that section of the cabin knew I would not switch seats with his wife. I then had to spend 5 hours sitting next to someone that sneered at me pretty much the whole flight.

I am generally a pretty nice guy. If they had even waited until I got on the plane and then made their case to me, I probably (begrudingly) would have switched seats with her.

Am I being unreasonable in feeling like these people were jerks? Their behavior sure seems rude to me.