Batman - do you like what you see?

the only reason we have not seen the joker do this is because that comic would never be published.

Looks like Joker really went through with sending Batman an image of him in a thong, just to verify his hypothesis from the Arkham Asylum game about what he truly fears.
(Never though a day would come where I could make a joke about that line, but I see I'm not the only person that vividly remembers it.)