I suppose that's a really good question. I mean, we are all different, so we can't just assume what freaks one person out freaks the next person out as well.
However, there are some pretty common fears that 'freak people out'.
Heights, for example. You go on vacation. Want to go to the top of the Sears Tower? No thank you. Want to go on this roller coaster with me? Yeah right. (You know, excluding the fear of roller coasters.) I'm taking a trip to Europe. Want to come with me? Do you mean that I have to fly?
Or there's spiders. Or anything that has more than four legs and doesn't bark or meow. Quite possibly snakes. Or mice. Clump those out into one giant cluster of things that can make some people take a step back.
What about water? I've known a couple people who are afraid to go in a pool unless they can stand on the bottom. Ocean? Probably not. Boat? Yeah, there's no point in even mentioning it. It'll be a no.
There are just certain things that freak people out. And there's nothing wrong with it because most people have that one odd thing that just tends to make them cringe. (And no, I'm not talking about nails on a chalkboard).
So what freaks you out?