For me for example its “Eat me - a natural and unnatural history of cannibalism” by Bill Schutt. Its an amazing book that covers cannibalism in animals and then the history of it in humans (cultural, survival & medicinal cannibalism).
I got a lot of “oh why would someone read something like that?” And “that not something fun to read about!” From relatives but my friends enjoyed the stuff that I could tell them about cannibalism!
We Wish to Inform You That Tomorrow We Will Be Killed with Our Families by Philip Gourevitch - about the Rwanda genocide. I always hesitate to recommend books I read about genocide in general just because it’s a dark topic.