A Flailer is one of those mysterious friends that one day just disappearers off your Facebook friend list without any reason. If you have a large friend list, you may never figure out who it was and why they deleted, blocked or whatevered you. Not only is it rude ,but may cause negative feelings and nobody wants that.
You keep adding new friends but the number stated on your home page always stays the same... or goes down! You keep seeing your "good friend from high school" name in your suggested friend box, but you know you have added them already...three times! They are "Flailing" cause they are: Flailers"!