“There are several reasons you might want to stage an unauthorized group exhibition inside the fifth-floor restrooms at the Museum of Modern Art: to attract attention, to poke a little fun at a powerful institution, to make a satirical point about the high-dollar commercial art world, to invite your friends to watch you pull off a good goofball stunt.” Such a show last week was, of course, “intended not so much for the fleeting moment as it was for the Web. “