A recent blog post listing various cases in which museum goers accidentally damaged art on display is amusing, but seems strangely silent where deliberate vandalism or "performance" is involved. Where's Tony Shafrazi's defacement of Guernica? All the efforts over the years to destroy the Mona Lisa? Where's the Fountain?
While attempts by Pierre Pinoncelli and others to damage or "intervene with" Duchamp's urinal may not qualify as accidents, they definitely count as occasions when the relationship between art, spectator and museum was "mangled." Likewise, the inclusion of the Fountain itself into a museum context originally mangled something.