I am walking behind a greasy grad student who is twirling his pointy umbrella as if there is no tomorrow. I know that he knows that I'm walking behind him. I saw him glance back.
Then at an intersection, he turns as if he's going to cross the street. I walk past him. After a few paces I hear the crunching of leaves on the sidewalk. Out of the corner of my eye, I see him resuming his walk, behind me.
That just totally creeps me out.
But at least I know where the emergency phones are. I also have my own umbrella in my hand. And I know how to use it.