Day to celebrate King Charles II escape from Cromwell's troups during the English Civil War. Held on 29th May, his birthday. you are meant to wear a sprig of oak. in the olden days if you didn't do this then young boys could pinch your bottom hence is was known as Pinch-Bum Day. The Chelsea pensioners celebrate the day by drinking beer and eating plum pudding. Charles II over ruled Cromwell's ban on merry-making and invented this day for people to party.