A phrase mocking any token or procedure the possession or performance of which invests a person with arbitrary authority.

It's a nod to the specific criteria necessary for the Pope to be said to be exercising Papal Infallibility -- and so be speaking for God. Without fulfilling the criteria he's just a man in a funny hat and can be as wrong any anyone else.
"I don't need to look it up. I'm wearing my infallible underpants."

"For Christ's sake Bob, you've a clipboard not infallible underpants."
by jamiebabe July 21, 2015
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