I'm sure I'll rustle some jimmies with these, but two I've always hated are Apocalypse Now and Tombstone.
For Apocalypse Now, I'll defend myself by saying that before I saw the movie, I was forced to read Heart of Darkness by Joseph Conrad in school. That was the most awful book I have ever read, perhaps (outside of obvious awful shit like Jane Eyre, Pride & Prejudice, Twilight, etc.). And I had to know it forward and backward for the fucking Academic Decathlon. I hated it so much. And then I watched Apocalypse Now a few years later, and realized they straight up copied almost all of the major aspects of the book. I typically like war movies, even weird ones, and I always liked all the Sheens, so it is possible that I might have enjoyed the movie at least a little if I never read that book, but since I had...I'd rather have my fingernails pulled out than watch that again.
Tombstone...again, I love Kurt Russell. I loved Val Kilmer, and his scenes I would happily still rewatch thousands of times. I typically even like westerns. But there are parts of that movie that are just fucking retarded, and the part that cemented it for me (we saw it in theaters) was the shitty montage sequence of hunting down all the red bandana (or whatever it was) wearing bandits. I've only ever seen it the one time, so my memory is very hazy now, but I remember saying "What the fuck is this?" in the middle of that montage. My best friend agrees with me (he saw it at the same time). Literally every other person I've ever spoken to loves the movie. We are on an island alone on this one, it seems. A no homo island.