Marina Abramovic, Rhythm 0, 1974
This was a 6 hour performance. Laid out on a table were 72 objects the audience could manipulate in any way they wanted to upon her body. As time passed, the audience became more and more aggressive towards her and by the end she was injured and violated; her clothes taken off her body. Many of the audience members were frightened when she cut off the performance; they thought she would retaliate.
She was confronting the audience and raising their awareness about their potential for violence, particularly towards women. They placed their desires onto her passive and inert body.
The MoMA website has a good slideshow/audio presentation on the piece: http://www.moma.org/explore/multimedia/audios/190/1972
This was, by far, one of the greatest performance art pieces of the 20th century. Listening to her account of the performance is chilling and yet, inspiring, as one can really get a sense of her extraordinary commitment to her art. This piece was able to communicate and question how we treat one another, women especially, more efficiently and succinctly than a great number of scholars, which is the sheer beauty of art.