You gotta know the magic deletion words. Otherwise, it just proliferates when well-meaning people start adding posts, and then the thread takes on a life of its own, and everything goes completely out of control.
They're encoded in the Newbie Guide, IIRC, once you figure out the substitution cypher and the key to which lines are important. Sorta like the invisible room that lots of people know about, but about ten folks can figure out how to consistently get back there.