Create your own haiku, never publish it. What are the odds of someone creating exactly the same haiku?

Probably much higher than you suspect. Making password haikus is an obvious idea which has been suggested many times before.

I'm sure that even with a great statistical model of password haikus (say an LLM) yours would still be one in a billion which still seems unlikely, but a cracking cluster can try billions per second.

In these cases it's very easy to have security that depends on the odds that a powerful attacker just hasn't gotten around to seriously trying the broad class of predictable generation schemes you've used.