Bad apple

Meaning

A single person who can spoil the reputation of a whole group.

Usage

Used when isolating someone who causes trouble.

Origin & History

Origins and dates here are approximate summaries. Many idioms have disputed or unknown origins, and not every date has been checked against a historical dictionary, so treat specific dates and stories as a starting point rather than a citation.

Observation that one rotten apple spoils the barrel.

Appears in moral warnings since the 18th century.