Now I wholeheartedly believe in finishing what you started, but sometimes there have to be exceptions. I mean if you get the sun lounger and a cold drink out and the thought of reading more of the book turns you cold – I think you should stop. If you are not enjoying it put it back on the shelf, or give it to someone who will enjoy it. Books are there for your enjoyment, they shouldn’t be a chore.
However saying that and going back to my original point, if you have only a couple of chapters left, get rid of that apathy and man-up. The satisfaction of completing a book that was challenging will be greater than if you cave. In the end I guess it all comes down to you.