I have two. The Ritual and Drowning.
The Ritual is pure smut. 61 chapters and every one contains a graphic, demeaning sex scene. I’m convinced the author was an adult film screenwriter and decided to try their hand at writing a novel. There isn’t a single likable character in this book.
Drowning isn’t a great work of literature. I felt that the characters were very two-dimensional. I hated how naive the author made the protagonist. It made me have a lack of sympathy for her. The ending was series finale of Dexter bad.
The Wall by Marlen Haushofer. The premise is kind of interesting. A women goes to the Alps and gets trapped behind some kind of invisible forcefield which blocks her off from the rest of the world, so she has to survive on her own. The book unfortunately ended up being a monotonous slog. It made it especially boring that the protagonist was not curious at all about the origin of the forcefield. She didn’t try to experiment or learn about it. Instead she was just like: “OK, I am going to take this cow to go grazing again and come back.” Not interesting at all.