By Kurt Vonnegut, from his book Timequake:
That the impulse to laugh at healthy people who nonetheless fall down is by no means universal, however, was brought to my attention unpleasantly at a performance of Swan Lake by the Royal Ballet in London, England... A ballerina, dancing on her toes, went deedly-deedly-deedly into the wings as she was supposed to do. But then there was a sound backstage as though she had put her foot in a bucket and then gone down an iron stairway with her foot still in the bucket.
I instantly laughed like hell.
I was the only person to do so.
A similar incident happened at a performance of the Indianapolis Symphony Orchestra when I was a kid. It didn't involve me, though, and it wasn't about laughter. There was this piece of music that was getting louder and louder, and that was supposed to stop all of a sudden.
There was this woman in the same row with me, maybe ten seats away. She was talking to a friend during the crescendo, and she had to get louder and louder, too. The music stopped. She shrieked, "I FRY MINE IN BUTTER!"
It has been almost two years since the death of Kurt Vonnegut. I'm still sad that there won't be more books from him.