The Backstage bar, a rough and ready little liquor-laced hideaway that calls itself "the best dive bar in the world," is known as the oldest bar in Culver City and celebrates its 75th anniversary this year. Across the street from Sony Pictures Studios, it has the distinction of being the watering hole of choice for the notoriously rowdy Munchkins during the filming of "The Wizard of Oz." It's not a fancy mixology bar, but the drinks are good, strong and low-priced, and head bartender Steve Chen will mix up whatever poison you happen to name, even if he has to make it up. That's how Chen invented a nifty refresher called the AFF, a bestseller at the Backstage and its sister bar Mom's, which recently opened in the old Del's Saloon space on Santa Monica Boulevard and Bundy Drive. Chen says the name is short for the unprintable praise that a woman looking for a new cocktail lavished upon the drink when Chen handed it to her. It was something close to "Absolutely fabulous!"