This painting is a masterpiece in the "Girls Gone Wild" portrait series of ancient times.
Long before the invention of the camera, degenerate low lifes (such as Degas) would lurk amongst Spring Break revelers and quickly paint young women drunkenly exposing themselves.
Having perhaps had "one too many" this young woman moons the observer. Ironically she only ends up making an ass of herself. She'll look back on this moment as a low point in her life, of having hit bottom - so to speak.
Young girls are very impressionable and that is perhaps why Impressionists, such as Degas, are more successful at these sorts of paintings. In addition, the quick brush work of Impressionism was a great advantage for those wishing to capture these fleeting moments.
This painting (and others in the series) serve today as a cautionary tale of wild abandon and the repercussions thereof.
-- Sister Randy