This is a fun thread. I love reading about the books people have hated.
I've read some bad books, but the ones that bother me the most are those that are supposed to be well written by authors that will get promoted no matter what they write. At the top of that list for me is "The Blind Assassin" by Margaret Atwood.
Being a good Canadian I've read all her books, which really makes me more of a good masochist because I don't like much of her stuff. But, The Blind Assassin was rediculous.