FSM, Cthulu, pink unicorns, &c, are epistemic examples of faulty reasoning. They draw a parallel between belief in God and belief in the FSM. They're meant to clarify. Nobody actually believes in them.
People don't believe in the FSM
because there's no evidence for it. Atheists don't believe in God for exactly the same reason. If disbelief in the FSM is reasonable, so is disbelief in God, yet theists constantly fail to see the parallel.
Flying Spaghetti Monster - Wikipedia
What evidence do you have for the non-existence of the FSM? See the corollary?
This is another of our recurring beefs with theists. They don't understand burden of proof. They keep asking for evidence where none is needed.
Non-belief is logically assumed in the absence of evidence, it's the default.