The ear jokes, identical jokes. Just so much. And the part where Ron says to Hermione 'No wonder I couldn't get my wand out Hermione, you packed my old jeans, they're to tight.' LMAO, too funny.
And Pottercast, how one of the twins says that they didn't agree on that name. lol.

There were so many great lines! JKR is such a funny writer... I give her so much credit, it's so hard to transfer humor to paper. Definitely loved Ron's "Merlin's saggy left --" exclamation, and "runs faster than Severus Snape chased by a shampoo bottle". The description of Sirius's room made me laugh, as did Potterwatch, and basically all of the ear jokes.

I can't remember them all, there are so many funny parts to the book.

My favorite scene that made me laugh was by Mrs. Weasly:
"GET AWAY FROM MY DAUGHTER YOU *****!"

The Potterwatch radio show was hillarious! and all the holey jokes made by Fred and George! The part when Ron is trying to stop rain in Yaxley's office, was v.funny. Also, when McGonagall charmed the desks in the battle scene she yells "charge". Also, Snape's scarastic humour when he's talking to Dumbledore about killing him.
When Harry was in Sirius's bedroom where there were pictures of bikini-clad girls, lol!

When Ginny getting mad when some other girl was flirting with Harry.
When Ron and Hermione kissing in the middle of the battle in front of Harry.
And when Ron returned and he was getting yelled at by Hermione just after saving Harry's life!!!