I think mine’s Z for Zachariah. The book is insane. A psychological survivalist thriller between a 14 year old girl and a strange man with unknown intent. The movie is… not this. They changed everything meaningful about the characters and lost all the tension. Hope someone does it properly one day. What’s your adaptation peeve?
Masters of the Universe, not that the source material was any good (in my defense I was a toddler when I liked it) but the movie is batshit insane in a totally different way and may as well have been it’s own thing.