The date is June 1215. As a condition of signing the Magna Carta, John has somewhat reluctantly, agreed to anger management therapy.
The Facts
To say that John had anger management issues is an understatement. He really did smack his friend in the face with a chess board. There was no love lost between him and his Brother Richard either. He did throw Arthur's supporters into Corfe Castle and starved them to death. It is also highly likely that Arthur was killed under his orders by being thrown into the Seine with a big rock.
The description from the Chancellor of what John was like in a rage is a verbatim quote. He fell out with the Pope (another understatement) and England went through a period of not being able to attend church or any of their ceremonies such as weddings or funerals.
He did order the deaths of 28 hostages in Wales as well as throwing various people in prison to die. He did indeed write to the Pope to get the Magna Carta repealed.