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?
Bad as in so different from the book I would say The Lovely Bones but I think it was much better than the book, which I never say but it tricked me into reading the book which I immensely did not enjoy at all and as an adaptation goes it really was so so different than the book.
As far as bad as in like bad movie and bad adaptation I have to echo I, Robot