This book is a stand-out, "that's a couple of days of my life I will never get back" example for me. (Note: I couldn't remember the name of the book or the author, and luckily her surname is at the beginning of the Wiki list of Oz female authors of fiction so I found her details within seconds.)

Glenda Adams: Dancing on Coral

It won an award, it had a blurb which talked it up to the max, and I persisted through it, thinking it would possibly redeem itself by the end, but no!

I read it in the late 80's when I worked in the local public library. I still vividly remember that never-to-be-repeated experience and every time I saw the book on the shelves I would get that same dragging feeling again.

Since then, if a book is grinding slowly forward, not progressing, I skip to the end and read that to see if it is worth reading the rest of the book.

Disclaimer: other readers might have loved it. Not me.