Peculiarly caught and hoisted

From dictionary.com's Word of the Day for July 7:

Shibboleth is from Hebrew shibboleth, "stream, flood," from the use of this word in the Bible (Judges 12:4-6) as a test to distinguish Gileadites from Ephraimites, who could not say 'sh' but only 's' as in 'sibboleth'.

shibboleth \SHIB-uh-lith; -leth\, noun:

1. A peculiarity of pronunciation, behavior, mode of dress, etc., that distinguishes a particular group of persons.
2. A slogan; a catchword.
3. A common saying or belief with little current meaning or truth.

Accustomed to the veneer of noise, to the shibboleths of promotion, public relations, and market research, society is suspicious of those who value silence. –John Lahr

The fish oil shibboleth is only the latest to be overturned in recent years. Vitamin supplements and fibre have also been found to provide no benefits. –Nigel Hawkes, "Nice idea, but where's the proof?", Times (London), March 24, 2009

Class size is another shibboleth: First, small class sizes do not increase learning, and, second, class sizes have become quite small anyway. –Jay Nordlinger, "The Anti-Excusers", National Review, October 27, 2003

To illustrate the third sense more pointedly might be added something like:

Bible quoters who utter such shibboleths as "God hears and answers prayer" and "whoever believeth on His name shall have eternal life" are hoisted on their own Biblical petard.

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This post is dedicated to my cousin some times removed, Will B.