One that many here would probably consider obscene without any knowledge is "The Wedding dance" painted in 1566 by Pieter Bruegel the Elder.
The painting depicts a peasant wedding party and dancing which were forbidden by the church at that time. The Peasants got married and ran off into the woods to have their parties. The peasant class was seen as oversexed and overindulgent at that time and they reacted to the upper class derision with oversized codpieces as an insult to the upper classes.
Interestingly enough, this single painting could have more than paid off Detroit's immediate debt if the Detroit institute of art had been willing to sell it. It was recently appraised at $200 million.
