Kelly Clarkson and her brother made a splash the other night at the Mandarin Oriental. As the pop cutie sipped white wine with party promoter Jay Galvin and Jason Clarkson, “the brother suddenly spilled a glass of whiskey all over himself,” reports The Post’s Jana Winter. Then just before the stroke of midnight, Clarkson got up and announced to everybody within ear shot: “I have to go to bed. I have to sing tomorrow!”