what was the funniest thing about the Harry Potter books to you? it might be messed up of me, but for me it was the scene where Harry encounters Voldemort in the Ministry of Magic. "Don't waste your breath!" yelled Harry, his eyes screwed up against the pain in his scar, now more terrible than ever. "He can't herlar you from here!" "Can't I, Potter?" said a high, cold voice. CAUGHT EM
There's a book where one of the twins said something about keeping their peckers up. In Britain pecker can mean spirit as in keep your spirits up. But since pecker is also slang for penis I always found that kind of funny in a juvenile way.
I forgot where this came from (it might be from OotP), but I found one particular Divination class funny in a juvenile way too. (Not verbatim all the way) Lavender Brown (looking through a telescope): Oh, Professor, I think I've seen an undiscovered star! Professor Trelawney: That is Uranus, my dear. Ron Weasley: Can I have a look at Uranus too, Lavender?
For me its any of the innuendos. Like this one from Order of the Phoenix "Hermione was reading the Daily Prophet again, Ginny was doing a quiz in the Quibbler, and Neville was stroking his Mimbulus Mimbletonia which had grown a great deal over the year and now made odd crooning noises when touched."