What it means
The British twin of loose lips sink ships, another wartime poster slogan warning that a stray word in a pub or on a bus might reach the enemy. It survives as a tongue-in-cheek nudge to keep sensitive news to yourself before it spreads.
Usage examples
"Careful what you say at the bar about the redundancies, careless talk costs lives and half the office drinks in here."
"Don't post the holiday dates online, careless talk costs lives."
"He clammed up about the merger, muttering that careless talk costs lives."
Where it comes from
Lifted straight from a British Second World War poster campaign, which warned that a stray remark overheard in public could feed enemy ears. The slogan outlived the war as a wry reminder to keep quiet.
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