From ajokeaday.com, though I first heard a version of this thirty years ago.
Bill, Jim and Scott were at a convention together and were sharing a large suite on the top of a 75-story skyscraper. After a long day of meetings they were shocked to hear that the elevators in their hotel were broken and they would have to climb 75 flights of stairs to get to their room.
Bill said to Jim and Scott, “Let’s break the monotony of this unpleasant task by concentrating on something interesting. I’ll tell jokes for 25 flights; Jim can sing songs for 25 flights; and Scott can tell sad stories the rest of the way.”
The others agreed this was a good idea so Bill told jokes for 25 flights, recalling the best of those he’d read at The Laughing Housewife.
At the 26th floor Bill stopped telling jokes and Jim began to sing.
At the 51st floor Jim stopped singing and Scott began to tell sad stories. At the 74th floor he said, “I will tell my saddest story yet…I left the room key in the car!”