I’m not sure if this rule was invented or discovered and I don’t know who did it, but it works. In geometry, it takes 2 points to make a line. And in comedy, it takes a 3rd point to make a punch line. The first 2 points create a pattern or rhythm, and the 3rd point is the misdirection.
The easiest way to do this is making a list of threes. For example, you can say, “There are 3 things in this world that scare me: cockroaches, rats, and my mother-in-law.”
The first two on the list takes the audience going in the direction of normal things that scare people. The third is where it becomes absurd. The generic pattern there was – animal, animal, person (or animal depending on how your relationship with your in-law is).
Let’s use another example to beat the dead horse. I don’t get the metaphors women use when they have their period. They say things like, “Aunt Flow is visiting this week”, “Aunt Red is in town”, or “My vagina is bleeding”.
I think you get the point. Let’s stop the bleeding.
List making is just one way of using the rule of threes in comedy. You can also write jokes using 2 beats or sentences for the setup and doing the punch line on the 3rd beat. An example would be:
My parents separated because they didn’t get along. My mom wanted a responsible man. And my dad was responsible for taking home a different woman every night.
Okay, not the best joke I’ve written but it shows how to write in 3 sentences using the first two for the premise or setup and the last sentence for the punch.
This rule of threes for writing jokes has been around for a long time and it will be around forever. Use it.