After Prince Philip and Princess Aurora/Briar Rose have met and done their little dance/duet, the way Prince Philip then asked "Who are you?", and in such a casual manner, is hilarious. Her reaction is even better. She sounds so surprised.
The following exchange between Flora and Fauna:
Fauna: (propping up a sagging 15-layer cake with a broom handle) Well, what do you think of it? Flora: Well, it's...it's a very unusual cake, isn't it? Fauna: Yes... (the cake frosting begins to flow down the broomstick, taking the lit candles with it, and Fauna scrambles to put them back on top) Of course, it'll be much stiffer after it's baked!
The blue-pink color fight between Flora and Merryweather, particularly when Maleficent's pet raven looks in the chimney to investigate the commotion and then gets shot in the face and the rear.
Plus the part after the aforementioned color fight when Aurora's dress gets turned into a Picasso.
Fauna:(reading recipe for a cake) "Two eggs, fold in gently." ...fold? (shrugs, then folds in two eggs— shell and all)
Her shocked expression when she hears the crunch really sells it. She knows something's wrong.
Fauna: Yeast, one tsp. (pronounces as "tisp") Tsp?
The fairies attempt to make a dress, with Merriweather as the "dummy." It's all in Flora's deadpan delivery:
Merryweather: It looks awful.
Flora: That's because it's on you, dear.
By the time Flora finishes the dress, it looks as short and plump as Merryweather instead of tall and thin, the sleeves have become too skinny for Merryweather to stick her arms into, and color-clashing pins and ribbons remain visible against the pink fabric. Merryweather looks utterly miserable while modeling it.
King Stefen and King Hubert having a drink. And then starting to have a brief argument (complete with Hubert using a fish as a weapon), which quickly dies and replace with laughter. During the scene, the minstrel sneaks a drink for himself a few times, and ends up drunk. By the end, he's passed out under the table, with his head stuck in the guitar. Try to keep a straight face as he snores in that thing!
Apparently, in the search for Aurora, Maleficent's goons hunted for a baby for 16 years. Even Maleficent seemed to find it funny... at first.