That's just Dini's writing which as time has gone on, I've grown to hate. His Joker is a clown, literally, and a vain one at that who hates being laughed at or easily bullied into an action. His Joker isn't a force of nature or an unstoppable madman like Nolan's Joker who wins even when he loses. He isn't the fluid, fluctuating bipolar Joker like the comics portray him, where his attitude and personality are dictated by how he feels (and how he's being written).
Put simply, after revisiting Batman: The Animated Series and the movies, and in light of the HILARIOUS The Killing Joke adaptation with the riotous scenes of torture and the humerous implications that Joker is literally raping Batgirl (instead of that being a cute undertone), I have grown to hate Paul Dini now. And reading this topic reminded me of why- he writes Joker like a turbo-charged Cesar Romero expy and that sucks.
Mark Hamill's still the best Joker.