MADISON, Wis. — A Wisconsin man defending himself against homicide charges for allegedly plowing his SUV through a Christmas parade stripped off his shirt, sat with his back to the camera and stuck a sign he’d been given to signal objections down his pants Thursday before opening statements began in his trial.Prosecutors allege Darrell Brooks, 40, killed six people and injured scores of others on Nov. 21 in the Milwaukee suburb of Waukesha. Police said he turned into the parade after fleeing a domestic …