Kevin Federline is looking back at a moment that changed his marriage to Britney Spears for good. According to People on Friday, the 47-year-old former dancer wrote in his memoir, You Thought You Knew, about an argument the former couple got into over him smoking weed in their house. Britney revealed in her own book that she "couldn't stand being around pot smoke," to the point where "even the smell of it nauseated" her.