Via Boing Boing comes a modern work of art commemorating a historical incident in which female transportee prisoners conducted a mass mooning of a prison official:

female prisoners in Tasmania mooning a prison official and slapping their naked butts

As the story goes:

“…on a sudden the three hundred women turned right round and at one impulse pulled up their clothes shewing their naked posteriors which they simultaneously smacked with their hands making a loud and not very musical noise.”