In trying to bring justice to England, Henry II brought about one of history's most infamous murders. Henry VII dusted off an outdated law and ate his way to power. Writing two laws a day, Joseph II of Austria failed to please most of his people most of the time, and brought his empire to the brink of revolution.
When the love of his life died, Henry III of France went on a binge of free spending, cross-dressing, and self-flagellation, until he got himself killed. Peter the Great dragged Russia out of the Dark Ages yet had his own dark side: he collected freaks of nature, and took a personal interest in torture.
A royal affair could be a dangerous liaison. Anne Boleyn flirted with Henry VIII and lost her head. England's Princess Caroline had flings on the side, like her husband, George IV, but fell victim to double standards. France's Louis XV was the lustiest monarch in history, and paid for it with his life.