20-some years ago, when I was about 11-12, I had this happen to me. Every once in a while, my family and I went to dinner at one particular restaurant, and every time we went, I saw the same man there. He was always alone, and he always stared at me, watched every move I made, with this very creepy half-grin/smirk on his face. He made me very uncomfortable.
At the mall one day with my mother and grandmother, I saw the same man in the store. I didn't think he'd seen me, so in order to get away, I told my mother I was going to Record Town. I was wrong - the man followed me. As I was looking through the bins, he positioned himself on the opposite aisle, facing me, but between me and the door. Every time I moved further down, he moved with me. And he wasn't looking at the records - he was flipping through the bin, but staring at me out of the corner of his eye with the same creepy half-grin as always. After my mother showed up, he continued to stare and follow us until we left the mall. I don't remember when I finally lost the guy, but thankfully, I haven't seen him since I was a teenager.