Nothing scares me, because I used to think I was indestructible. Now I know I'm indestructible, not to mention my spine is indestructible. It's all titanium.
The original 'RoboCop' was X-rated, and then they had to cut it down so it became R-rated, and Verhoeven claimed that actually made the movie more violent, because it's what you don't see that actually scares you.
I use myself as a measuring yardstick, and so if I come up with an idea that really scares me, then I'd like to think that people out there would feel the same way as well.