What is the absolute scariest horror movie you've ever seen?

The scariest movie I've seen to date is called "It Follows". I was surprised at how often my heart was racing because I'm a real horror fan and usually nothing really scares me too badly (and the synopsis of the movie looks awful tbh... I thought it would be a throwaway film) because I watch so much of it. But that movie is like really unsettling and just fills you with dread the whole time... it's great!! And really well done. And the music was rad too. When I was a kid I saw The Exorcist and I was scared to DEATH for MONTHS and couldn't sleep but then I rewatched it last year and it was actually just really hilarious...it made me laugh so much!! So my "Scariest Movie Ever" shifted from something that is like outright supposed to be scaaaary and grotesque, to something that was way more subtle, which has... nothing to do with the question I'm posting but it's interesting to me so I thought...that... I would share it. :) Anyway, whats yours?