What is the term for a follower of the (formerly purely rhetorical) religion of the Flying Spaghetti Monster?
Pastafarianism.
Pastafarianism is the religion. A pastafarian is a follower.
Ah. Thank you both.
Or you can just call us Monstrosities. It was originally intended as an insult by our detractors, but like the Quakers before us, we felt the path of true humility was to accept and even celebrate the term.
There’s also the Church of the Frequent Flying Spaghetti Monster (FFSM.) It’s mostly the same, but you get points for going to church.
I will point out that True Believers in Invisible Pink Unicornianity have no truck with all these newfangled cults. 
What about pirates?