The concept would be based on the recently added "People You May Know" feature, the same one that has been on LinkedIn for quite some time now. You know, the freaky list of people that you "should" connect with, because they happen to be on the list of your friends, or friends-of-your-friends? I am actually pretty amazed how well LinkedIn has been able to make it work, it's almost freaky to see some ghosts from the past re-appearing.
The idea of "You Suck" app is that there is a reason why those people are not on your friends' list. You may not want to have them "friend" you on Facebook! Hello, anyone thought of that?!
So, the "You Suck" app would use the list of "People You May Know". Then, let's say Brian would be on the top of my list, begging me to connect to him. After all, he is already friend with 5 of my friends. Then there would be Mary, Ann, etc.
Now, it's time to calculate the "You Suck" value for Brian. From me, he gets 5 "You Suck" points. Brian might be on the "People You May Know" list from some other people too. So, similarly, we would count those values and add them up.
Then, next time when Brian logs in to his Facebook account, among other nice and positive things about the world, he will be able to check how much he sucks to me and other People He May Know.
Now, talking about a killer app?
Facebook has quietly rolled out a new feature called “People You May Know”, which, as the names suggests, attempts to identify members of the social networking site who you likely know but haven’t actually “connected” with yet i.e. invited to be a “friend.” ZDNet