I love to collect vintage/antique books and my favorite terrible cover that I own is for a copy of The Road Through The Wall by Shirley Jackson. It's about an upper middle class neighborhood where people are upset that a wall separating them from lower class homes will be torn down. There's also a mystery about a missing child. The cover shows a couple embracing with a tantalizing tag line "A married woman prowls the back streets!" It has almost nothing to do with the actual book and I fear anyone who picked it up based on the cover will believe it's some sort of romance when it definitely isn't.