I have had this thing happening to me a couple of times here.
You meet some in some group activity and have fun together and a great conversation.
We add each other on Facebook.
Then we do not meet up so often.
One day you run into them somewhere.
They do not even recognize you, though you are friends on Facebook.
Sometimes, I introduce myself and remind them (because I remember quite well) where we met but they generally do not sound convinced.
I delete them from Facebook.
They still do not recognize me when they run into me again!
Strange, how we are friends on Facebook but we do not even recognize them in person!
Note: This post was triggered because I ran into this girl yesterday and she did not even recognize me, but we have been running into each other quite often this past month and I know her and even reintroduced myself to her and still she does not remember me.