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?
A bit of recency bias with this one, Killers of the Flower Moon. One of the most intense, gripping true crime books became a haphazard snooze fest - the story, the cast, the director, all pointed to it being a banger. But I was forgetting the movie as I was watching it.