I've taken up several policies about books considered to be classics.
First, I force myself to start books that I wouldn't normally read, but I don't force myself to continue reading them. If I'm not feeling a book after the first 25-50 pages, I'll set it aside, no hard feelings. I've taken up this policy after I realized how my own mood and where I was in life affect my reading preferences. For example, when I was younger, books in which involve marriage issues would have held no interest for me. Now that I'm married I can read about some of the Big Problems in a fictional character's marriage and identify in them my little problems.
Secondly, I'll give a book that I set aside a second chance after awhile. I started Cryptonomicon several times, but it was just too big to get through. It wasn't until I got the chance to sit on the beach for a half-week and get into the story that I really enjoyed it.
Lastly, I'll never say I hate any classic book. I think if the book is highly considered enough to gain the label "classic", then a number of people see something good about the book that I'm not seeing. I might not understand some aspect that others see in the book; I might be in the wrong mood or setting to enjoy it; the book might not be "the one" for me. Sometimes a book isn't that great on its own, but is important for a historical reason, like being the first of a certain genre. Whatever the case, if a book is a classic, it at least deserves some respect, though not my love. I'll feel free to criticize it or not enjoy it, but I won't claim superiority over all my fellow man by kicking it out of the canon.