The best time was for me on an international flight. I was flying by myself at the time and the Flight Attendant comes to me and asks if I would not mind switching seats with a passenger who needed to be next to his son. The Father was upgraded to First Class but not the son and for some reason the son was afraid to sit alone.

I said sure. The Father thanked me profusely and said that I would enjoy my seat. He even gave me a $20 to boot(not that I needed it). I was put in a lie flat First Class Seat and enjoyed my flight.