If someone in authority reads the riot act or reads someone the riot act, they angrily tell someone off for having done something stupid or wrong. I'm glad you read the riot act to Billy. He's still a kid, you know. He still needs to be told what to do. At the weekly cabinet meeting the following day, an enraged Mr Schroder read his ministers the riot act. Note: The Riot Act was a law passed in Britain in 1715. It made it an offence for a group of twelve or more people to refuse to break up and leave if someone in authority read them the relevant section of the Act.