Reading the Riot Act
Delinquent children, misbehaving students, errant employees… all may be “read the riot act.” It’s an idiomatic expression that we use when talking about forcefully warning or reprimanding someone.
Where did the expression come from? Turns out there really was a Riot Act – a British law enacted by Parliament in 1714 to discourage crowds from assembling and disturbing the peace. Per the law, a magistrate would read a short portion of the Act (something about the King demanding that protestors or rioters disperse immediately). If the crowd (defined by the Act as any group over 12) wasn’t gone within an hour, those still assembled were charged with a felony, potentially punishable by death.
(Source: Schott’s Original Miscellany)

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