Disproportionate Retribution: Mayor Hamilton Hill (who despises Batman) appears on television claiming that Batman and the Joker are equally as bad. Joker finds this comparison so insulting that (disguised as a party clown) he crashes a birthday party held at the mayor's estate for his son, Jordan, and attempts to blow up Jordan's birthday party (along with all the guests) with a stick of dynamite in the cake, just to see how "safe" his mansion is.
Dynamite Candle: The Joker has a fancy looking explosive candle on a cake for the Mayor's son's birthday party. While most of the guests don't suspect anything, Bruce realizes the danger and pushes the tray holding the cake into the swimming pool, where it harmlessly detonates in there.
Irony: Hill declares that his mansion is "safe" from the likes of the Joker, only for it to nearly get blown up by the Joker himself. Though Hill doesn't realize the irony.
It's All About Me: While not an extreme example, Hill wasn't too concerned about the well-being of his voters after the cake exploded. He was angry for being made a fool in front of them in his own home.
Lonely Rich Kid: Jordan Hill is the son of Gotham City's mayor, and his dad is so into his politics that he even used the kid's birthday bash as a political reunion. Jordan is so upset that he hides in the truck of the clown that the Hills hired for entertainment... not knowing that said clown was than The Joker under a disguise.