Officially today is Oak Apple Day...the day you wore an oak apple [acutally an oak wasp gall] pinned to your lapel to show your allegiance to the restored monarch King Charles II. Following the Battle of Worcester, Charles escaped the Roundheads by hiding in an oak tree...supposedly Major Carless had to keep tweaking the Royal Posterior to stop the fellow from dropping off! He was crowned on 29th May 1660.
Here in Sussex it was known as Pinch Bum Day. Traditionally the children were given a half day off school...if you didn't wear the oak apple then supposedly others could either give your buttocks a tweak or whip the back of your legs with nettles.
This folkloric tradition has now passed into the annals of history.