Cecil's reaction to the dancer transforming into a burly man.
There's also the Easter Egg regarding what's obviously an adult magazine found in the Dwarves' Castle. "Using" it prompts Cecil's overworld sprite to look in the four directions (akin to someone trying to hide something) before saying: "That's what I call a piece of literature!"
Also, Palom and Porom's antics.
Waking Yang up from his coma is a great laugh in itself.
Cecil: My friend, I ask for your forgiveness...
Before that, we have Cecil's thoughts during the Sylph Cave.
Cecil: Of course! With this we can... cook something?
Who could forget the immortal Woolseyism from Tellah?
After exposing the Fake King plot, Paladin Cecil can join in a dance with Baron's Dancing Girl. And in the DS version, it's absolutely hilarious; armor-clad, gallant, Bishounen Cecil copies all of the girl's movements; from the hops to the waves, to the hip thrusts. It tops even the Dancing Girl Surprise in Fabul.