It's made up out of whole cloth, part of The Game:
Catholic: We believe this.
Catholic-hater: Oh no you do not believe that, you believe what I say you believe. Don't deny it!
Catholic: But we know what we--
Catholic-hater: Silence, papist!
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Except that it really isn't a game, is it? Since we Papists have no chance of "winning"? Just today I saw a post that for the millionth time asked if Catholics don't read the Bible.