Had a FAA guy, DC-10 typed, ride the jumpseat back in the CRJ days.

ATC gave us a lower altitude so I looked at the release, which had the lower alt. and also entered the change in the FMS.

He then spoke up by saying in a higher than thou attitude, "Welllllllll, I'm not familiar with the CRJ but how do you know what your fuel burn will be now?"

I then showed him my release that had the new altitude, and the began to give him a lesson on the FMS and actually showed him how little fuel the aircraft burn even if they dropped us down to 8000 ft.

He remained quiet for the rest of the trip and a few days later I ran into some fellow FAA folks from this guys region and told them the story. They just rolled their eyes and said that this guy was a real winner.