I smile at people if I think I know them or if they are smiling at me. I have a dreadful habit of not being able to place people sometimes, which can be rather embarassing socially.
Eg. Once on the street this guy smiled at me, I recognise him and smiled back, he greets me, we start talking. All the time I'm desperately trying to remember where I know him from. So I stick to general topics - how's work, family etc. Nothing, a complete blank. I finally confess I have no idea who he is and he admits he was having me on and tells me I was in the front row of a play he was in the night before.
