Everything is wrong with this picture! Rather than a draped symposiast, a nude woman reclines (spayed rather unbecomingly) on a striped pillow, her uplifted index finger hooked into the handle of an enormous skyphos (quite a different type of drinking cup than the shallow kylix this image decorates).
She is apparently attempting ‘kottabos’, one of the most popular drinking games in 5th century Athens. The player typically twirled a nearly empty kylix, aiming to shoot the silty dregs at a target: a little balancing disk, basket, floating vessel or even a companions’s head. This feat of dexterity with a deep skyphos would have been physically impossible (something like shooting darts with a baseball bat).
So the spectacle of a lady attempting this manly target practice with a ridiculous cup and stark naked to boot was supposed to read as a big visual joke to the guy who saw it in the bottom of his cup: ‘Women! They just can’t get it right!’
