The worst I've had myself was the audiobooks of the Lensman series, by E. E. "Doc" Smith. It's old classic sci-fi, which I like, but I'd never read that series. I saw the whole thing was available on audiobook, and went ahead and got them all. I started listening in the car, as I drove to work.

They started reading the preface/introduction/whatever, and talking about the author, and how the story inspired other space opera, and the Green Lantern comic books, which I knew, and then just casually talked about the plot of not just the first book, but the whole damned series. Like "This happens in book one, and it looks like it's resolved when that happens, but this comes back in book 2, and it gets resolved like this. But then, in book 3, this other thing happens, and it's tied to this thing in book one, and that doesn't get resolved until this character from book 2 does this thing in book 4, and ..."

If I wanted that, I'd have read the Cliff's Notes, not bought the book. And it's an audiobook, so skipping the introduction isn't really an option, particularly while I'm driving. What the hell were they thinking? I mean, it's early pulp space opera, so you know most of the stuff that's going to happen is just "The protagonist is the best of the best at anything he tries, and science can do anything", but you shouldn't know the details before they happen.