My Sister's Keeper. I will NEVER forgive them. It was my favorite book as a kid and they completely f*cked it up and changed crucial things in the movie.
Hunger Games was almost on point but they didn't include Madge who played a big role in the first book and Katniss' character development. #JusticeForMadge
Queen of the Damned was wrecked in the transition to the screen. The book is so dense and layered and they just lamely threw it and elements of The Vampire Lestat together to make some quick MTV-generation cash-in that bore no tonal resemblance to the source material.