all mouth and trousers

• all mouth and no trousers

mouth, meaning "talk" rather than action and trousers, presumably at the time of origin a reference to masculinity, either as trousers as a male item of clothing, or a reference to the genitals.

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all mouth and trousers (not comparable)

1. (Britain, idiomatic) Superficial, engaging in empty, boastful talk, but not of real substance.

• all hat and no cattle

• “All mouth and trousers” in Michael Quinion, Ballyhoo, Buckaroo, and Spuds: Ingenious Tales of Words and Their Origins, Washington, D.C.: Smithsonian Books in association with Penguin Books, 2004, →ISBN.