When I was like 3 I was on my own watching daytime TV and they showed a clip of Ghostbusters where Slimer flies at the camera screaming and I had nightmares for ages! Imagining unstoppable ghosts coming screaming through the walls at me. Years later I find out it's a comedy and it's great but yeah.
In honor of scary media month: what is the first piece of media you remember truly frightening you as a child?