What do you do when someone friend requests you that you don't know?

Confirm them as a friend and then never bother talking to them. Hey look at you with all those friends! Damn you're popular.

Click "Ignore" and go about your business. I don't give a crap who they are...don't know 'em, don't care to know 'em.

Send them a message asking who the hell they are and why the hell they friend requested you.

Let 'em pile up in your friend requests list...maybe they'll go away sooner or later. Then if you happen to meet them at a later date and they say "Hey why didn't you accept my friend request?", you say, "Oh, I didn't check my list." Riiight.