People who carry weapons
This is a no brainer. People with weapons can get angry and hurt you with their weapons. It may even be an accident. Weapons are dangerous if they are not handled properly.
Dangerous criminals and terrorists
I have never met one and I hope I never will come across one. They are the most twisted people in society. They might have dangerous plans and I don't want to be one of the victims.
Dead people (ghosts)
So many stories of dead people haunting places. I actually wonder if they are true or not.
They still exist. The scary part is that you can't tell if someone is a cannibal or not because it can be one of their secrets on the deep web. I'll be scared if I find out that someone I know is a cannibal.
That woman creeps me out and has put fear into me throughout my childhood. She has schizophrenia and has tried to kill me because of her delusions.
I guess most of these scare most people.