I'd go with the unknown.
Edit: I changed my mind, I now picked feminazis.[spoiler]jk feminazis are a joke[/spoiler][spoiler]I don't know what my biggest fear is[/spoiler]
-
Well, Freud theorized that our great fear was castration anxiety. Male children want to eliminate their fathers and marry their mothers. But they're afraid their father will find out about this and cut off... certain parts. So they decide to be "just like Dad" to please their father, so that hopefully he won't neuter them.