I once attempted to read a SF novel called 'Midshipman's Hope' by David Feintuch. I had read a review that said that it was entertaining and original ... or something. It was none of the things that the reviewer said it was (I'm convinced that he hadn't read the same book!). It was turgid, badly written and very poorly visualised.
It was set on some sort of spaceship which was part of some sort of navy of the future. The ship's senior officers seemed to spend most of their time flogging the junior officers. Descriptions of flogging, and vague discussions on the ethics of flogging, went on for page after page until I realised that I was reading a sort of inept, sadomasochistic porno novel. I ripped the thing in half and flung it across the room.
The above was one of the worst books that I have ever (attempted to) read but the 'Da Vinci' code is also high on the list.