My babysitter showed me Critters (in secret) when I was 5. Rather than be scarred, she turned me into a avid horror fan. I saw all the 80's classics when I was way too young for them thanks to HBO and Cinemax.
None phased me.
Laughably, what finally got me was so mild. In Poltergeist 2 or 3, there's a scene where the kid's reflection no longer mimics his own movements. It's not even the scare, but rather the set-up.
I started staring at mirrors when I was alone, just waiting for my reflection to break into a sinister smile. My fear was, when it did, what would I do? No adult would believe me. Mirrors are unavoidable. Something supernatural would be after me. I knew I wouldn't be able to pull off some "final girl" shit IRL.