Originally Posted by Homer J. Fong
I take it that he in the moment when he looks into the plastic surgeon's mirror, he snaps. He's not trying to convince himself that he looks good as a coping mechanism, he truly does think that, he does embrace it, he uses this as a way to start remaking himself and then Gotham. I'm not rejecting complexity or hidden meanings, but I think that when he says, "I'm the world's first fully functioning homicidal artist," that's exactly it. In one of the Simpsons flashback episodes, Marge hands Homer a picture that Bart's just drawn, which we don't see, and Homer looks, then huddles and screams, "Send it to Hell!" I think that's essentially this Joker, an artist who now has the means and ability to pursue his vision. A vision that's the most twisted, gruesome joke.
I think you've summarised it well. We were shown that Jack Napier was into art early in the film as well. He has art in his apartment, he is very concerned with his fashion and style. Almost similar to American Psycho
yuppie-style obsession with aesthetics.