It's interesting to work in a face to face customer service industry for some time. We had regular customers at Barnes & Noble 7 years ago. Some are now regulars at the Starbucks that I work at and remember me from back then.
Others I see when I go walking at the mall in the morning. This is an interesting situation. We are not friends, we do not know each other, even though we saw each other every day for 2 years. Without the counter and the coffee, there is nothing.
Except... You can tell that they know you from somewhere. There are about 4 different people that walk at the mall that I had a regulars back in the day. A couple I even remember their drinks or how they ordered.
Now we silently pass each other every morning in the mall with an extended glance of, "Don't I know you from somewhere?"
It goes the other way too. There is a lady that walks at the mall that also works at the Smith's that I shop at. I have friendly customer service conversations with her at Smith's maybe 2-3 times a week. But walking in the mall, we just pass each other like we've never seen each other in our lives.
I'd say something to them, but then you start a whole thing. Do you then have to talk to them every morning when you go to walk? Say hi, wave, nod? Just easier to be silent I guess. Odd.