Facebook Unicorn
A Facebook Unicorn is like a ghost from your past. You see them on Facebook, you know who they are, but when you actually talk to them, you feel like you're talking to a ghost.
Hey. We went to the same party. I think you vomited on my shoes.
Oh my God. You're that guy from the yearbook. Why are you still alive?
You're the one who added me at 3 AM. I still don't know why.