The execution of this person is the origin of the phrase: "Laughing your head off."
Mary, Queen of Scots
The execution of Simon "the Fox" Fraser, 11th Lord Lovat and Scottish Jacobite leader of Clan Fraser. Just before he was to be decapitated at the Tower of London, April 9, 1747, for treason a scaffold holding spectators collapsed, killing and injuring at least 20 people. This accident caused Fraser to start laughing. He was still laughing when the headsman’s axe came down.