I was on a flight from Glasgow to Philadelphia and was sitting on the row of seats at the front door.
The stewardesses were just about to close the door when 2 guys walked from further back on the plane, stopped the doors being closed and said "we don't feel like flying today". They were let out of the plane, without any questioning.
I was thinking "that was weird" and "it'll probably delay the plane by the time they get their luggage removed" but the doors were shut, the plane taxied and we took off on schedule.

Feel free to post your terrifying/strange/unique flight experiences in this thread.
CHAT allowed.
I'm not a nervous flyer, but I have never been so relieved to touch down!