Awesome Discworld Funny Heartwarming TearJerker WMG YMMV
The moment you realise that Creosote, Nijel and Conina have stolen the horses of the Horsemen of the Apocralypse.
The reactions of the horses' owners, too.
Vetinari getting turned into a newt. He gets better.
The entire part where the four horsemen, or rather one horseman and three pedestrians, get drunk.
The bit when a voice speaks up in Rincewind's mind, saying "You rather like her, donít you? I can tell", and the exchange afterwards. It was his libido speaking.
"Laugh This One Off". Funny to everyone, except the poor sap beneath the slab (or the poor sap who just missed getting hit by it).
Rincewind trying to build a tower in his sleep while Creosote, Conina, and Nijel watch him incompetently do so.
"Rincewind carefully tried to balance a large rock on a small pebble. It fell off, but he appeared to be happy with the result."
What the Librarian is doing to a damaged book: an Appendixectomy.
When the heroes come across the mind-controlled Abrim, and Nijel searches his instruction book for how to deal with the undead. Turns out vampires can be defeated with garlic, whereas for zombies you need sea salt and lemon—
Conina: We're trying to kill him, not cook him!