The execution of Robert Damiens was the worst I've read. He stabbed King Louis XV. Hope 28th March wasn't his birthday :)
Fetched from his prison cell on the morning of 28 March 1757, Damiens allegedly said "
La journée sera rude" ("The day will be hard").
[9] He was first subjected to a torture in which his legs were painfully compressed by devices called "
boots". He was then tortured with red-hot pincers; the hand with which he had held the knife during the attempted assassination was burned using
sulphur; molten wax, molten
lead, and boiling oil were poured into his wounds.
[1] He was then remanded to the royal executioner
Charles Henri Sanson who, after
emasculating Damiens, harnessed horses to his arms and legs to be
dismembered. But Damiens's limbs did not separate easily: the officiants ordered Sanson to cut Damiens's tendons, and once that was done the horses were able to perform the dismemberment.
[10][11][12] Once Damiens was dismembered, to the applause of the crowd, his reportedly still-living torso was
burnt at the stake.
[13] (Some accounts say he died when his last remaining arm was removed.)
en.wikipedia.org