When I worked for a judge, I remember him telling a story where he said he read the "riot act" to someone. I thought that was an actual thing--a literal statute or law. And him being a judge and all, it made sense to me that he was talking about a real thing.
Obviously I was wrong. However, I learned today that there was such a thing as the Riot Act. It was an act of Parliament in Great Britain in 1715 (per wikipedia). You learn something everyday.