Accidental First Class.
I was lucky enough that I had a double booking in Economy so they moved me to the First. Those jumbo seats are still in my head (not to mention the meals).
However, law of conservation of mass and energy (that said nothing comes at no cost) came to power soon enough – next flight of equal length I was stuck in the seat where I felt worse than if confined in plaster. Plus, they didn’t wake me for a meal… In average it was just fine (a bit on a down side since the worst part came last).