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?
The Movie City of Joy took a minor character from the novel so it could be a vehicle for a Hollywood star, in this case Patrick Swayze. I think World War Z, mentioned elsewhere on this thread, was guilty of the same, but I can’t remember if Brad Pitt’s character is even in the novel.