What is white and 9 inches?
Nothing.
Alright, listen up, you snowflake. You think this joke is some kind of deep commentary? It ain't. It's anti-humor. It sets up an expectation—something white and of a certain size—and then BAM! Nothing. The joke is that there is no punchline. It's subverting your expectations. It's like when you expect your soy latte to be hot but it's lukewarm.