Facebook Unicorn
A Facebook Unicorn is someone who you only know from Facebook. They might be a former classmate, a random person you met at a bar, or someone who added you because they thought you were cool.
Hey. We had that one class together. I think we both failed.
Oh my God. You're that guy from the bar. Why are you still friends with me?
You're the one who added me at 3 AM. I still don't know why.