In some East Asian cultures, your wedding gift should be in an odd number. (Even numbers could be easily split in case of divorce.)
A British official fulminated in 1946 that a displaced person was one who could be repatriated. Someone who refused repatriation was a refugee, entitled to asylum but not assistance. Therefore they should stop the displaced person camps and stop feeding them.
In the Soviet Union, there were persistent folk legends that Isaac Newton and Abraham Lincoln were Jews.
Spinel was synthesized by accident in the 18th century.
When Eisenhower ordered Patton to go around Trier because it could not be taken with less than four divisions, Patton sent back a message that he had taken it with two, and what did Eisenhower want -- for him to give it back?
When Catherine of Aragon died, both Henry VIII and Anne Boleyn wore yellow -- that being the color of mourning in Spain.
The USSR, to keep a veneer of legality about admissions to college (for some reason), would ask undesirable elements "coffin problems" that were immensely difficult to figure out the solution to. (Easy once you know it.)
When the USA proposed that Jewish displaced persons go to the Middle East after WWII, other Allies accused them of wanting to make Europe as "Jew-Free" as the Nazis did. (Also that their decisions were influenced by the NYC mayoralty election -- probably true.)
Romans insisted that though they used crucifixion as the ultimate penalty, they didn't invent it. A crude and barbaric people -- Assyrians, Gauls, Persians -- had done it.
Because British nobles of high rank had an accumulation of titles (picked up by the family over centuries or decades as they rose to their high rank), the heir apparent is called by a courtesy title of the (generally) next highest subsidiary title. Sometimes, by a writ of acceleration, he can actually hold the title and sit in the House of Lords.
When Scotland tried to lure skilled Flemish weavers, they laid down the law that they were "take no apprentices but Scottish boys and maidens of this realm, and before any others, the burgesses' bairns of Edinburgh."
That the Germans used the single Enigma machine during WWII helped Allied cryptoanalysis. Not only did they have a larger group of text to work with, that they could decode them if they broke it helped garner support.