I don't know, I see it kind of like Puck disguising himself as dull as dishwater Owen from Gargoyles.
Joker is a lot of things; a harmless trickster, a deranged killer, an incomprehensible force of chaos, but never a straight man.
A fact that he was secretly running a hate group that singles out people who aren't "average", when the Joker is the most abnormal person in the room, is probably hilarious to him.