To explain the concept of post-modernism to your friends I recommend you show them the SBS documentary ‘Is This Shit Art?’ about the Belgian artist Wim Delvoye who manufacturers artificial shit and calls it art. He sells the shit for 1500 Euros a piece.
A tongue-in-cheek view of the shit machine can be found here:
A more serious business view:
Have a look at Delyoye’s amazing site here: http://www.wimdelvoye.be/