Not suprisingly, I have a few.
I'm going with the Problem Child Series, The Mummy, Sliver, and The Lost World: Jurassic Park.
Here's the thing: I loved Jurassic Park. I've read everything by Michael Chricton and was way excited for the film, but there was a problem – no one who made the movie read the novel. They just had an illiterate drum-playing monkey skim the book and the monkey retold the story to the screenwriter in sign language, but the screenwriter was blind, so he just made up some crap and Spielberg was like, "a'ight, wrastle up them dinosaurs!" and they made a movie.