Well, this is something I've always wondered about myself...I remember hearing Yoko Ono talk about the first time she met John Lennon; he'd attended one of her "exhibits" at the the-groovy Indica gallery in Soho. There was an apple on a pedestal, and he took a bite of it. Yoko was outraged and said something like "How dare you touch my piece?" She immediately put him down as a philistine, but apparently changed her opinion later. Of course, their short (!) film on the process of tumescence is another instance of art possibly taking the piss......