Throughout all of the intervening 979 days: I have no contact at all with this friend-of-a-friend, and that's not a surprise because I have nothing in common with him at all other than the fact that we share a friend in common.
To the best of my knowledge he knows nothing about me -- I certainly know nothing about him.
Yesterday: I get an email notification that he's requested to add me as a friend on Facebook. This email arrives at an email address I don't routinely use, that I never hand out. There's nothing in the invitation to identify the source other than the person's name, a name which is completely unfamiliar to me. If I go to Facebook, I can't do anything (such as looking him up to find out about him) without signing up for the site.
Fortunately I'm good at searching through old emails, and I discover that he's the complete stranger with whom I had a single contact nearly three years ago.
He still knows nothing about me, to the best of my knowledge. However, I now know one crucial piece of extra information about him: He's a tosser, a complete idiot.
There's a new rule in my mail filters referring to "Callum Mark Wright".
Edit: Clearly I'm having a bad day.