You mean its not to activate an exploding bomb in a goon's stomach?
i was always against that idea that that is whats realy going to happen. i always thought it was because he was mocking someone. other than that this is how i think the scene is going down:
the joker says evening commissioner to gordan as he walks in.
the mayor than comes in to announce that gordan is the new commissioner and that the joker is the one that killed loeb.
the joker mockingly claps about that.
is it weird that out of all the joker scenes we've seen so far the one that scares me is when his licking his lips in the scene where he faces batman in the batpod? the one in the new imax featurette