The only time I've ever felt threatened involved a crazy person.
In the perceptions of others, franksolich has actually been in dread physical peril too many times to count, but as I wasn't aware of it myself and came to no harm, it all just went right over me.
But there was this one time a guy about 18 years old, but a whooping couple of inches taller than me (I'm 6'3", no dwarf) approached me, having wandered away from his mother. He looked normal, other than his height and his weird eyes.
Looking at me with those dead eyes, he kept repeating something over and over again, the same words ("this is ****ed, this is ****ed, this is ****ed, this is ****ed," or something similar with that). Even though I was just a harmless person merely standing there, he made sudden threatening moves at me.
I grabbed a moderately-sized crowbar that was at hand, but then his mother came over and calmed him down. He withered into a sobbing wimp.
After she bound him inside the car, she explained to me that he was mentally-ill, and had been spending the holiday (the 4th of July) with the family. He lived in a nuthouse in South Dakota, and resented that he had to go back.
Whew. A close call, because that overaged child could've creamed me, easily.
I for one think there's very sound and valid reasons for cops to be apprehensive about the mentally-ill.
I know if I were a cop and spied the subway cat, I'd be hoping I was wearing brown pants.