Customers line up for lunch at John Mueller Black Box Barbecue in Georgetown. (Photo ©Chris Wilkins/Texas BBQ Posse) You can say a lot of things about John Mueller, who some might call the bad boy of Texas barbecue. And, over the years, most of it probably has been said. But the dude can cook! We were reminded of that during a recent visit to a new trailer operation — John Mueller Black Box Barbecue — in Georgetown. “Damn, he’s good,” I blurted, after taking a bite of Mueller’s smoked turkey. I followed with a crusted bite of fatty brisket. Delicious.…