Nothing goes together like karaoke and Flaming Dr. Peppers — that is, except for crooning and martinis. So if you're ready to trade in the Journey for some Sinatra, head down to the Mission/Hayes Valley border joint, Martuni's. Seven nights a week, the back room of the bar features a professional piano player and mike for any patron who'd like to play Bing Crosby for a night. The feel of the place, however, is more sing-along than American Idol audition. The regulars — mostly gay, mostly middle-aged, and mostly good crooners themselves — are there to hang around the piano and sip one of the bar's 15 versions of the Bay Area's greatest contribution to cocktails: the martini. At Christmas time, the place is a veritable circus, with local takes on the traditional sing-along like "The 12 Sex Toys of Christmas." Martuni's is the kind of place that harks back to the more musically vibrant San Francisco of an era gone by: a place where you could walk down the street any given night of the week, wander into a bar, and hear some good music — or even make some yourself.