One of the things I like about the Joker is his improvisation in the moment. How he manages to turn almost any situation to his favour.
The ending of B89 shows this really well, I think. Batman is on the warpath, and is the better fighter. But Joker keeps the gags going, ala his chattering teeth. He puts on his glasses, is punched and seemingly falls to his death. But then Batman and Vicki are the ones fighting for their lives. And he then lends Vicki a 'hand'.
You think the gags are harmless - and most are. But it's the one that isn't which catches you off guard.