Written by DCist fashion contributor Rachel Cothran. Find more of her writing at her web site Project Beltway. Mauro Farinelli’s favorite word is ass. “Your ass looks hot,” he tells me, pronouncing it the same way you’d say “ouch” after stepping on something sharp. “You have a great ass,” he determines matter-of-factly. And what Farinelli says, goes. The thirtysomething owner of local jeans mecca Denim Bar has a magnetic personality and the certain know-it-all attitude…