Batman's greatest rogues often serve as warped reflections of the man himself. They symbolise key parts of the Caped Crusader's fears and personality traits. The Joker is well aware of this, going to extreme lengths in his bid to prove he and Batman are inherently similar. One could almost call him a troll, given his crimes are oft-perpetrated to incite a reaction from his nemesis above all else.
The Joker's obsession with Batman might keep him oddly safe from murder most of the time but he's the exception. The lives of others clearly mean nothing to Gotham's court jester. Guilty of every crime they have a law for, the killer clown haunts the crime-ridden city like no other.
While many of the Joker's most depraved acts have occurred on page, he's saved a few for his countless adventures on the big and small screens. A curious running theme throughout the Joker's big screen dalliances is his impact on the city at large. Whenever the madman shows up, it seems the whole town goes to hell before all is said and done.
One of the greatest menaces in the history of fiction, there's no shortage of unspeakable acts where Mr J's concerned.