Trogdoor
When walking the halls one day, one observant KGB member found a door lying on its side in the A level of Porter Hall. Knowing immediately that he could use this door to impress a girl, he recruited help in transporting the door from Porter Hall to the CS Lounge. There he removed from the door every bit that was easily removable.
That night, with many loyal comrades in tow, the industrious hero of this story took the door out to the Cut. There they gave it legs to prop it up and they adorned it with beautiful words. The things it said included, "Trog" (hence the name, Trogdoor), "Art is this" (referring to an earlier postering campaign which involved sheets of paper adorning various objects asking, "Is this art?"), and a French phrase meaning "This is not a door".
The door stayed on the Cut for a week. Toward the end of that time, it started showing up in strange places (first it was in a tree, and next in a flowerbed) until finally it disappeared entirely.
Some time later, the aforementioned hero of the story was talking to an Art grad student. He discreetly asked whether the student had seen the door, and it turns out that the student had hated it, describing it as everything that was wrong with CMU's art program.
And so the hero was happy with what he had wrought.