What is the scariest experience youve had in a movie theater? – The A.V. Club

My first thought was also Hereditary, which chilled me to my very core when I saw it at Sundance; I was so freaked out by it that I actually considered fleeing the theatera very rare sensation for me, and one that I tried to honor when I sat down to write about it later that night. (On some level, I do think that I fed this movies hype machine with that dispatch, which the trailer quoted, and feelperhaps rather arrogantlysomewhat responsible for the number of people who later reported that it wasnt so scary, what was all the fuss about?) But if Im honest, there was no single moment in Hereditary that shook me as fast and forcefully as a two-second shot from the American version of The Ring. Its the moment when we see, very briefly, what Samara did to the girl in the opening scene. That cut to the closet, and into a close-up of the dead girl inside of it, was so unexpected and so horrifying that I spent the rest of the movie in a state of sweaty panic, convinced they were going to pull the trick on me again, that it was only a matter of time before wed get another shock cut to another pasty, grimacing corpse. It haunted me. Not bad for a PG-13 Hollywood remake. [A.A. Dowd]

More here:
What is the scariest experience youve had in a movie theater? - The A.V. Club