I never saw the original thread. I think it came from a joke, where someone compared the warm fuzzy feelings of the holy ghost with having a soft lovable ferret shoved up your bunghole. It then grew from there.
YOU don't know the ferret thing? It's now integral to RfM. I think it was scooter who started it, but I'm not sure and too lazy to look it up. But it was a thread about how Mormons go to and fro through this life telling people how to live it, while being a TBM was like having a ferret hanging halfway out of your ass. Then they tell people, "Pay no mind to the ferret hanging out of my ass!"
Call it a take on the whole New Testament beam and mote meme.
I haven't been around for a while so I missed that one when it first came around.
Now, "ferret" will be in the same part of the lexicon as "pickle" - both of them will conjure up images that will render me temporarily hysterical with laughter.