badatthis great way to handle your problem. You were much more diplomatic than I was a couple of weeks ago. My wife and I were flying on a flight from Charlotte to Chicago that we were not able to make because the originating flight was late.
We were bookd in middle seats on the next flight out. Not the best option but we had to get to Chicago. We joked about which seat each would get and who would sit next to the "fat guy". We both boarded and took seats with no-one else in our rows.
First comes the guy next to me sitting by the window. He must have been 6'2" and 300 lbs. It was workable since he knew he was large and sat close to the wall - a gentleman. The guy in the aisle seat must have weighed 400 lbs.
He was so large he brought his own extra long seat belt extender. My wife was turning red trying to stifle laughter. He immediatly tried to put his carryon in front of my seat and raise the arm rest. No being shy, I told him to move his bag to his seat and I pushed the armrest down and stared at him.
He tried to sit in his seat but just plain wouldn't fit. He squeezed and finally got close enough to the seat where he could buckle the extended belt. For the entire flight I sat on the edge of the seat closest to him making sure he wouldn't "appropriate" the seat I had paid for.
The F/A's were grinning the whole time. Luckily it was a relatively short flight. He never said a world as we left.
If I were a longer flight I would have gotten the F/A involved but it worked out for me.
I do agree that the airlines should follow through on any rules they have established regarding oversived passengers and not rely upon the person sitting next to them to complain.