This design is based in the comic The Killing Jocke, in whitch Jocker tries his best to drive Batman mad as he’s. As Jocker said: “All it takes is one bad day to reduce the sanest man alive to lunacy. That’s how far the world is from where I am. Just one bad day.” It’s a recurrent idea in the Batman series that Jocker and Batman aren’t that different; after all, the idea of a man disguissed as a bat and going out on the street like this every night does not sound sane at all.