Joker dies bcs during his big dramatic speech of the day he tries to be be all insane and funny by pretending to shoot himself in the head with his BANG! flag gun but he fucks up getting distracted by flirting with Batman and mixes up his guns and he shoots himself in the face in front of the bats. Jason, who was being bodily held back from shooting him himself by Bruce and Dick for the past 15 minutes, laughs so hard he fractures a rib and has to be carried back to the batmobile