Stick with me, this can get confusing for those who aren't highly verbal and good with spatial concepts. "Flying Spaghetti Monster" (FSM) is another word for "everything." The Flying Spaghetti Monster equals everything. Everthing is The Flying Spaghetti Monster. To deny that "He" exists is silly because the universe and everything in it exists. Thus, atheism is prepostorous if The Flying Spaghetti Monster is everything.
The only question (and it is a valid question) is whether Everything when taken as a whole is sentient or not.
In other words, does The Flying Spaghetti Monster (or "everything" if you prefer) think? Does The Flying Spaghetti Monster have a plan? Or is Everything (i.e. his noodly appendages) just ... here?
Some people prefer to believe that Everything is just randomness with no plan. "Everything" is just does its thing with no guiding force, no rules, no anything. Everything, of course in an ever changing but non-planned form, has always been here. Everything will always been here. Everything is nicely organized into protons and electrons and stars and galaxies (did you know that superclusters of galaxies are shaped exactly like spaghetti threads, coincidence?) Lives come and go with no meaning whatsoever. All of this and more is "Everything".
Some people have come to realize that Everything seems to have a design and a plan, and that the Grand Architect planned everything. Some people (Einstein included) believe that time is an illusion and that the infinitely complex organizational structure of Everything implies one undeniable conclusion: Everything (or The Flying Spaghetti Monster) is sentient. The The Flying Spaghetti Monster has a plan. That plan is far more complicated than we can possibly imagine or understand.