This is kind of lame (and TV rather than movie), but I guess I had a sheltered upbringing, and I was just six.
1977 was the heyday of Alice Cooper. As a sophisticated adult, I can now appreciate the antics of Alice for what they were, and even stifle a yawn at them. But as an impressionable six-year-old, not so much.
The scene that scared me was nothing about Satan worship, or fans dismembering chickens. It was, of all things, an award show, at the end of which Alice saw fit to pull a gun. The host (was it Dionne Warwick?) shrieked, the credits rolled, and I was terrified that Mayhem had seemingly intruded on the propriety of Hollywood.
Yes, Michaelis Maus, I was already inhabiting The Matrix.
For a couple of years after, Alice Cooper was at the lead of my personal pantheon of hobgoblins. I was scared that he would break into my home and subject me to some unspeakable horror. (I don’t know what that horror would have been; singing School’s out for summer, I expect.) I went so far as to bow my head while in the toilet, convinced that that would prevent Alice from identifying me, and whisking me away to some sort of un-education camp.
I’m pretty sure you couldn’t pull that kind of stunt these days. It truly was a more innocent time.