A person who vehemently denies that any of us can truly know anything spiritual. An anti-religious nag who is every bit as annoying as bible beaters.
Typically, this person is a pain in the ass and harps on the same discrepancies in the Christian bible that every is well aware of.
"I just felt so inspired, like God was guiding me."
"You can't say that! You don't know God is real! Prove it!"
"Stop being such a nagnostic, you jerk."