i've always been pretty good with scary stuff, at least in media, but one thing that really upset me as a child was one scene in the Spawn animated tv series where a priest kills someone by dropping a grenade into their pants and i think just the absurdity and the fact that it happened to a completely random person going about their day was something my 7 year old brain wasn't ready to cope with lol.
the only thing i can think of that's kind of gotten me in my adult years is one scene in Inland Empire with the demon with a horrifically distorted Laura Dern face.
as for things i've read i don't have a ton of experience with horror books but there's a SA scene in Black Flame by Gretchen Felker-Martin that really made me squirm.