Read me the Riot Act
I like etymology; my roommates' first language is not English and I frequently find myself explaining some of the phrases and words that I use. One of my favorites is the "reading the riot act." Like many English terms, I had no clue where it came from. I stumbled across this in a book I'm reading:
The British Riot Act of 1714
Our Sovereign Lord the King chargeth and commandeth all persons, being assembled, immediately to disperse themselves, and peaceably to depart to their habitations, or to their lawful business, upon the pains contained in the Act made in the first year of King George the First for preventing tumults and riotous assemblies. God Save the King.
Once a magistrate reads this passage to an unruly mob (of 12 persons or more), they have 1 hour to disperse. Once the "riot act" was read (it must be read precisely) and the hour has passed, their prescense ceased being a misdemeanor and became a felony (possibly punishable by death). It was repealed in 1973.