Holy Blood
The book drove me crazy because I seldom came to a page where I didn't know they were wrong. So much of what was in that book was made up from whole cloth, or was taken out of context, or was simply a lie that I had trouble finishing it. They made up research, they used sources they knew to be fake, and they ignored all sorts of things.
If you actually do the research yourself, it soon gets laughable. Even people they interviewed were ignored when something was said they didn't want to hear, and sometimes they "quoted" the person as saying the exact opposite of what was really said.
This book didn't get blasted by the experts because it was controversial, but because it was utter nonsense. It's one of those cases where even if everything in the book is true, the research they say supports it is false. It's also a case where you can't believe what you read. Any historian can tear the book to shreds in minutes, but the average reader doesn't know enough history, or doesn't have the time and energy to check all the sources and backtrack the research, to know what to believe and what not to believe.
I like controversial books, but I prefer it when everything in the book is honest, when interviewees are quoted correctly, and when only real historical documents are used.