Fleeting Demographic Rule

1. A gimmick or storyline may be reused freely and safely after a few years of dormancy.

2. The unwritten rule that, after a given number of years, there has been enough turnover in the fanbase that a writer can re-use the same gimmicks and storylines with impunity.

The fleeting demographic rule allows YouTubers to reuse jokes and catchphrases after they have become repetitive.