This idiom signifies being caught in an embarrassing, vulnerable, or compromising situation, often unexpectedly, leaving one exposed or unprepared. It implies a loss of dignity or control, typically due to a mistake or oversight, and is used in contexts ranging from personal blunders to professional or moral failings. The phrase carries a humorous or slightly scandalous tone, evoking the literal image of being caught undressed, but it often describes figurative exposure, such as being unprepared or guilty of misconduct.

The phrase likely originated in early 20th-century American slang, rooted in the literal embarrassment of being caught with one’s trousers down, possibly in intimate or private moments. It first appeared in print in the 1920s, with a 1923 *Chicago Tribune* article using ‘caught with his pants down’ to describe a politician surprised by a scandal. The phrase gained popularity during the Jazz Age, reflecting a cultural shift toward more candid expressions. By the mid-20th century, it was common in journalism and literature, as seen in John Steinbeck’s works, to describe public or private humiliations. Its spread to British English and beyond reflects its universal appeal as a vivid metaphor for vulnerability.