Last mention of Facebook I promise

One thing which has surprised me about Facebook is the whole confirm/reject friend conundrum.
I mean, I like to think that there are parts of me which are able to act in a socially acceptable manner. So what is the socially acceptable response when someone asks to be my friend, but I have never interacted with them in any kind of meaningful manner?
Don't get me wrong, I have nothing against this particular person. I try not to have anything against anyone. Except John Cena.
But I have never exchanged small talk beyond monosyllables of greeting, never gone out for a beer with them, never met up to go to a movie, never emailed or texted them, never talked smack with them at a party, never misbehaved at the back of a rehearsal with them.
What is the correct response? I don't want to reject them, does this mean I confirm as a default option? Why can't there be a third option, and what would that third option be called? All I wanted was an easy way to stay in touch with my peeps when I am overseas...

Edit: okay, Russ's facebook analysis is much funnier.