Don’t expect a clone of Audrey Hepburn in this downtown update of Breakfast at Tiffany’s. Parker Posey doesn’t do imitations. She’s an original — smart, sexy and the scrappy comic force behind this playfully hip concoction from first-time director Daisy von Scherler Mayer, who co-wrote the script with Harry Birckmayer. Posey has been making herself known on the periphery — a soap stint on As the World Turns, a sly supporting turn as Darla the school despot in Dazed and Confused. Now the diva-in-waiting gets the star spot she deserves. Posey plays Mary, a party giver and goer who would rather dish with her Latin roommate (Guillermo Diaz), her gay designer pal (Anthony DeSando) and her falafel-vendor lover (Omar Townsend) than consider a real job. When an illegal rent party gets Mary busted, she persuades her librarian godmother (Sasha von Scherler, the director’s mother) to hire her. Mary’s choice is downtown or the Dewey Decimal system. That’s the slim plot. What makes it delicious fun is Posey, a party girl for the ages.