I didn't think it was Identity Crisis either since the Joker isn't even listed as a villain, but I found this:
http://rs362.rapidshare.com/files/88...Comics_737.cbr
I skimmed through it and couldn't find the Joker quote. Mind you I just skimmed, I have another paper (different psych class) that has priority over finding Joker quotes.
I will read through it again when I get the chance.