A few days ago I was walking to the subway and I ended up walking about a half block behind two young professional guys. I noticed that one of them kept looking back at me every few seconds and staring. It got to the point that I felt weird and thought I might have something on my face that he was looking at.
Anyway, I crossed the street so I wouldn’t have to catch up to them at the corner and walked the five or so blocks to the subway, forgetting about it for a few minutes. That is until I rounded the corner to go down the station steps and the guy who had been staring at me comes UP the steps from the darkness, walks past me, and makes two clicking sounds as he passed by me. No words, just clicks. He continued walking, and I, sufficiently weirded out, did exactly the same.