In the movie Trunchbull's line about playing a game called "who was wearing a pretty red, hair ribbon yesterday, and isn't wearing one today?". The line delivery can crack one up, even though it's probably not meant to be so funny. here
To clarify, in-context it's not meant to be funny, because of the reason she even has a red hair ribbon in the first place: Matilda accidentally left the ribbon behind at the Trunchbull's house after "haunting" her; the Trunchbull is trying to figure out which student she should punish. But, because of her delivery, the line becomes unintentionally hysterical.
Matilda's dad is full of hilarious moments, which isn't surprising since it's Danny DeVito playing him.
When Matilda first shows Miss Honey her powers, she makes a pitcher of water levitate. Miss Honey, deep in thought, pushes the pitcher back down without even noticing. Matilda then does it again and Miss Honey notices. The look of surprise on her face is adorably funny.
And then, when the Trunchbull walks in, the pitcher is still levitating, so Miss Honey grabs the handle and has to pretend she's just casually holding a pitcher of water there.
Matilda magically makes a glass of water containing a newt tip over onto the Trunchbull, and Trunchbull's desperate attempts to get the creature off of herself are hilarious.
After everything, Matilda decided to lampshade said moment to Lavender and Matilda imitating her "dance" when she tried to shake the newt off her chest.
Many, if not all scenes involving Mrs. Trunchbull when they aren't nightmarish.
WHY ARE ALL THESE WOMEN MARRIED?!
Your mommy...is a TWIT !!
Am I wrong? I'm never wrong. In this classroom, in this school, I am GOD!
In the book, the parrot scene is hilarious.
When Bruce Bogtrotter finishes eating the cake. It's funny because the score in that scene sounds like it belongs in an epic film. It's funny how it takes a scene where a boy is eating cake seriously.
From the musical, we have Agatha Trunchball's little... digression in the middle of 'The Smell of Rebellion'. Up till this point she's been singing about how she intends to weed out rebellious students from the school, and then suddenly she starts singing this. Full warning, It Makes Just As Much Sense In Context.
Miss Trunchbull: Imagine a world with no children/ Close your eyes and just dream./ Imagine... come on, try it, the peace and the quiet/ a bubbling stream/ Now imagine a woods with a cottage,/ and inside that cottage we find/ a dwarf called Zeke, a carnival freak/ who can fold paper hats with his mind, and he says/ Don't let them steal your horses, no!/ Don't let them throw them away, no!/ If you find your way through, they'll be waiting for you/ singing... neigh! Neiiigh!
Also from the musical, before Bruce starts eating the cake:
Miss Honey: Headmistress, he'll be sick!
Miss Trunchbull: He should have thought of that before he made a pact with Satan and decided to steal my cake!