I've just finished reading Tress of the Emerald Sea by Brandon Sanderson, and there were a few parts that got chuckles out of me. But there was one chapter specifically that had me cry-laughing for several minutes. I was reading it out loud to my wife and I had to stop every couple of sentences.
That led me to think of other funny situations in books. Discworld, as another example, usually gets a few chuckles out of me. So I want to hear some other examples, what's the hardest you've laughed at a book?
Edit: Thanks for all the suggestions!