The actual scariest stuff pretty much boils down to aggressive dogs being aggressive dogs.

For example: I saw a woman lose control of her pit-mix. The dog rushed over to one of our neighbors, unprovoked, and immediately latched on to her leg and started thrashing it. The dog's owner was freaking out screeching which seemed to agitate the dog rather than dissuade it from attacking. There was so much blood, but I think the only long term physical damage was scars. However, I only ever saw the victim once or twice after that, she stopped going out on walks after that event.

If you're willing to stretch the definition of scariest and seen:

Deer are super annoying sometimes. One of their behaviors is that they make a super loud snort-whistle noise when alarmed. So if you're outside and unaware of their presence, and especially if you're not expecting a super loud and almost alien-like snort-whistle coming from the woods right next to you, there's a good chance it's going to startle the crap out of you.