Been a long long while but basically empty flights were semi-regular things back in the day if you booked what you knew to be repositioning flights at odd hours.

I’ve been one of a handful of passengers more than a few times. Where the flight attendants just move everyone to first class after boarding and the rest of the flight is super relaxed and barely professional.

This was not common, but not a rare thing after the 2008 crash for a few years.

During IRROPs you can still luck into one of these. Definitely a fun experience!

Ha, I have. I was on the very first flight Jet2 airline ran after COVID lockdowns, and there were a grand total of 9 people on board of this Boeing 737 - it was surreal to say the least.