You know that obnoxious girl at the gym? The one that answers her cell phone while she's on the treadmill? Well, she would last about two seconds with Mickey Demos. The bad-ass, muscle-bound 44-year-old former boxing coach uses the same tough love, run-till-you-puke philosophy for his average Joe and Jane clients as he did for the late Golden Gloves champ Gus Rahming Jr. "I'll scream like a drill sergeant to get you beyond your limit," he says. "It doesn't matter if you're 5 or 75." In the past four years of training, he has gained a loyal following of gluttons for punishment. They range from high-powered lawyers to troubled street kids. His clients swear by his workout routine which includes a combination of cardio, weight training, and amateur boxing. He now works out of Extreme Gym on 71st Street and Collins Avenue in Miami Beach, charges $50 per hour, and plans to open his own gym this summer. Be sure to leave your cell phone at home.