This happened on a flight from Denver to Minneapolis.
The gentleman (and I use that term lightly) sitting behind us on the plane clearly knew everything about everything. While we were waiting for a gate to open, the woman next to him commented that the elevation on the TV said that we were at 400 ft. Mr. All-Knowing pointed out that "it is always way off. When we were on the ground in Denver it said we were at, like, 5000 ft!". I didn't say it, but I should have. "Let me guess, it was somewhere around 5280? Since that is the ELEVATION OF DENVER!" Some people are ridiculously dumb.