Expressing emotion in any way that’s real and meaningful is alien to the Joker, but he’s learning those parts of himself, however unconsciously, through Harley. On a physical level they’re dynamite together. A lot of relationships are defined by that. Two people may be really horrible for each other, but physically they push each other’s buttons so clearly they can’t get enough of that person.
Mark Hamill (on the JokerxHarley BtAS relationship), Batman: Animated
(Paul Dini, Chip Kidd, 1998)