late 80's, morning flight at San Juan delayed then cancelled. The delay kept getting longer. Later that night, I took a different flight on a different airline, not paid for by the airline. San Juan airport was too hot with no a/c in the main terminal.

FRA-JFK flight unable to land due to traffic. Landed at EWR, sat at a gate but the door open only a crack. Unable to deplane (didn't think of running away because of the possibility of arrest). Eventually flew to JFK about 5 hours later.

Travelled on Delta as an unaccompanied minor. Connecting flight cancelled. The agent gave me a hotel voucher and that's it. As a 10 year old kid, I had to get to the hotel, figure things out, and return to the airport the next day. That was in the days before the cell phone so I didn't think of calling home. I had 2 checked in bags and made the mistake of picking up only 1 bag, thinking the other one (with unimportant things) would travel on the plane the next day. The other bag was never again seen.

None of the above 3 instances were really terrible. However, the last might be a bit criminal. I thought it was a little fun.