Originally Posted by The Joker
He was a fun Joker when he needed to be. Whether he was sipping the guests champagne, stealing the hor dourves, dressing up as a nurse, going into a laughing fit when his own henchman gets electrocuted etc.
"All the old familiar places" he quips as he attacks Batman with the steel bar at the Prewitt building. He was very clearly enjoying it. We even catch him smiling when comes at Batman:
The Joker wouldn't have laughed UNTIL he saw the fireworks go off. He laughed when Batman threw him off the building because he thought he'd succeeded in corrupting Batman. Joker laughs when there's something to laugh at.
I'm sure you already know this, but the scene where he is beating Batman with the steel bar is a reference to the beating he gave to Jason Todd in " A death in the family"
Same camera angle too