mouth, meaning "talk" rather than action and trousers, meaning "showy clothes" i.e. outward or superficial appearance. The phrase originated in Northern England.
all mouth and trousers (not comparable)
- (UK, idiomatic) Superficial, engaging in empty, boastful talk, but not of real substance.
- "All mouth and trousers" in Michael Quinion, Ballyhoo, Buckaroo, and Spuds, 2004.