Alright, let's go.
Just because it's been mentioned already, but I quite liked Divergent. Insurgent and Allegiant, though, were almost offensively bad. I virtually never stop reading a book or trilogy once I've started, but Insurgent was so bad that I very nearly didn't read Allegiant at all. I did, and then wished I hadn't.
Twilight. Ok, I know I'm not the target audience, I also know that it's rarely the case that the best written books are the most popular. Nor should they be. People get all sorts of things from books, and guilty pleasures are par for the course. I also see the attraction in Twilight for the target audience. But for someone who isn't the target audience, Twilight is really, really bad. I didn't read the second one, nor will I ever.
For books that I am actually the target audience for, anything written by Dan Brown that isn't Da Vinci Code or Angels and Demons. Those two books, albeit having received far more attention than they deserve because of the religious controversy, are fine, surface level thrillers. The problem is that Dan Brown is a bad writer, and actively cannot write books outside of the same highly limited formula that resulted in those two books. Digital Fortress and Deception Point are entirely predictable when you've Da Vinci Code, because the plot is fundamentally the same. And then Lost Symbol might actually be the worst book I have ever read. It's just awful with no redeeming qualities at all. If there's one book that I would probably erase from existence entirely, it's the Lost Symbol.
More recently, I went on a bit of a classic sci fi binge, and was amazed at how good a lot of the classic novels are. There was, however, one glaring exception. Starship Troopers by Robert A Heinlein. Don't confuse it with the film. The film is brilliant sci fi satire. It has virtually nothing in common with the book at all, which is actually really quite serious military propaganda wrapped in a wafer thin plot. It's terrible, and I just don't understand why it's considered to be a sci fi classic when actual, stone cold classics like Childhood's End, Flowers for Algernon and I Am Legend exist.