Giving the Slip

Since the start of the Facebook craze, everyone with a profile has encountered this situation: someone less than savory from your past adds you as a friend. From then on, every time you see their picture or an update from them you wonder to yourself Why, oh WHY, did I add you to my friend list?!
Now what? How do you give someone the slip? Especially after they've sent you a message saying how good it is to see/hear from you. The guilt of the situation sets in and suddenly you're stuck. Sure, you accepted their friend invitation in the first place, but let's be honest, it was just to see what kind of a loser they've turned into; how many times they've been divorsed, how many kids with how many fathers they have, and the collective number of pounds gained since you last saw them (secretly hoping that it's in the ballpark of 300). But now, NOW you're trapped. They believe things are fine. It would be fine if they just sat there quietly in their profile and left you alone, but no, they have to be pleasantly chatty, just making the guilt even worse.
By guaging how bad you feel right now for adding someone just to see how big of a failure they are now, you know that if you were to "accidentally" delete them from your friend list you'd feel exponentially worse! The other option is a thoughtful rejection message, but that's not a good choice either since they will see it as totally unprovoked and suddenly the tables will turn. Next thing you know, a couple of months down the road the guilt will be eating away at you so strongly that you'll want to look at their profile "just to see how they're doing", suddenly feeling caring and considerate. So you send them a friend request, but they don't accept because, let's face it, you were kind of a dick. Now you feel hurt but can't help but believe you got what was coming. Lose-lose.