In 1919, Marcel Duchamp drew a moustache and goatee with a pencil on a post card reproduction of Leonardo's Mona Lisa, and named his work "L.H.O.O.Q." This, when read aloud in French, gives "Elle a chaud au cul", which means something like "She's got hot pants" or "She has a hot ass." He used an image, reproduced so often that it had become trite and mocked one of the most famous works in the history of painting.
Duchamp's work fell into an art movement that arose in Europe during World War I, known as Dada. This period came into being as a reaction against the unprecedented carnage of war. Artists felt that any civilization that could tolerate such brutality must be swept away, and all of its institutions, including traditional art, along with it. Dada, therefore, was against everything, and ultimately became the primary inspiration for the Surrealist movement.