Levi Johnston, ex-fiancee of famous teen mom Bristol Palin, admitted to Tyra Banks in an interview set to air Monday that the couple was not always practicing safe sex and says they shared a bedroom on occasion. Johnston talks about his relationship with Sarah Palin's daughter next Monday on "The Tyra Banks Show." In a preview, Johnston tells the host that he and Bristol were practicing safe sex, and agrees that her pregnancy must have resulted from some sort of 'wardrobe malfunction.' But when pressed by Tyra, he admits that they used protection "most of the time" -- but not...