It's disturbing to believe that he views exsistence, the world, people, culture, even himself as nothing but jokes.
It's why he's called the Joker, and why he does what he does. He's creating himself in view of his philosophy, that we're all jokes.
It's why in the comics he has variety to his crimes...some days he's a harmless prankster, the other days he's a homicidal lunatic. It's why he can commit so many different crimes...because it all borders on the theme that EVERYTHING is a joke.
Killing people and putting smiles on their faces, or letting them live to go insane like him.