Britney Spears is slamming ex-husband Kevin Federline's bombshell memoir! The former professional dancer's new book, You Thought You Knew, does not hit the shelves until October 21, but excerpts are already spilling out - and there's some shocking tea about his pop star ex! Per The New York Times, K-Fed is sounding the alarm in his memoir about Britney concerning behavior over the years, which includes claims that their sons, Sean and Jayden, are scared of her. Why is that? They allegedly told Kevin they saw "her standing silently in the doorway, watching them sleep ...