Tell us: what books are the most shocking or disturbing?

The Lovely Bones
Beasts of no nation (took a long time for a small book)
Smyrna 1922 (not fiction)

I'll say "Killer Fiction" by Gerard Schaefer. Serial killer short stories by a real serial killer. Thought by many to be thinly disguised retellings of his actual murders. I gave up about half way through it. It was just too ugly.

GUERILLAS by VS NAIPAUL
A HOUSE FOR MR BISWAS by VS NAIPAUL
HALF A LIFE by VS NAIPAUL

The first book of The Gap series by Steven R Donaldson.

Torture and sex slavery aren't my thing so I didn't finish the first book.

Mein Kampf Vol. 1 & 2, I read this in High School in the mid 60's, I bought it at a bookstore but did not let anyone know I was reading it because many people are very narrow minded and draw the wrong conclusions (I openly read Karl Marx's The Communist Manifesto and was called a "Commie" by other students). If the political leaders of the time had taken the time to read Mein Kampf, they would have had a good idea of who they were dealing with.
When I was a teen and also in my early 20's, I read a lot of political and philosophical books, now that I'm approaching 70, I read mostly "cozies" and mysteries.

That’s the one in the pool right?
I read the short story book, but it didn’t really stick with me.

The Woods Are Dark by Richard Laymon. The 1981 Warner Books version of this horror novel contains tons of explicit violence and rape. Lots of disturbing content. I've never read another horror book like this.

Some WWII history books. Antony Beevor's WWII in particular, he writes without filter, & rightly so. Some accounts of Japanese & Russian soldiers going full Neanderthal on populations in retreat &/or retaliation. Keeping in mind towards war's end, the armies were younger, teenagers, facing zero hope of much other than getting theirs. That's messed up. Armed & violent teens running over the global battlefields... not a great legacy of humanity.