Practically everything the Governance de Magi says while staging its council meetings. Especially Melchior's lines. In particular:
(The Governance de Magi is asking for volunteers to go after Rohoph)
Melchior: I'd go, but I need to wash my hair.
Gaspar: YOU DON'T FOOLIN' WELL HAVE ANY PRUNIN' HAIR, YOU LAGABOUTIN' SPOUTIN' POUTIN' TROUT!
Melchior: So it will take a very long time to wash it. You see, mathematically, since I have no hair, and dividing by zero results in infinity, it shall take an infinite amount of time to wash my hair.
After getting home from the Imagine Spot that is Mardek and Deugan saving a princess, the former's mother asks what you did. One of the choices in the dialogue tree has Mardek getting things a bit backwards.
Mardek: We slew a princess and saved a dragon!
Mardek: Well, I'd only kill a guy if he killed me first!
The encyclopedia's description of the zombie locksmith miniboss.
The 'Concerning Sirens' book found in Elwyen's house.
Concerning Sirens: I've heard they're dead sexy. Sexier than the sexiest human woman ever! I wish I could see one! I'd ogle it 'til the cows came home! Yowza! However, they're so dead sexy that they make you dead by being sexy. GET IT? BWAHAHAH! ...It made ME laugh! I wonder if this book will get published?
Concerning Sirens: Also, included on the following pages are sketches of Sirens. I'm sure THAT will get this book published!
Melchior: But what if they all use their soul transfer thingy-majigs?
Balthazar: I keep telling you: humans cannot do that, myes. They are weak and pathetic and they can't even perceive psychic energy waves or electromagnetic radiation.
Melchior: You have to believe, Balthy. You have to believe.
Take Vehrn and Elywen into the Dark Temple. Talk to Elywen. Do the same, but with Elwyen and Solaar. Laughter will ensue.
The Warport security is full of these. Answer a question wrong and the security person turns into a giant demon and kills you almost instantly. The best part is that they will call you a terrorist and then kill you if, for example, you say that the color blue is ugly, that you don't have enough legs, or that you don't find them attractive.