Cecil's reaction to the dancer transforming into a burly man made this troper snicker.
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 always made me laugh.
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?