One of Britney Spears' exes is coming after Kevin Federline over his upcoming memoir - and no, not Sam Asghari this time! As we previously covered, K-Fed is gearing up to release a tell-all book about his whirlwind romance with his ex-wife and baby mama. It's called You Thought You Knew. And although the memoir doesn't drop until October 21, some shocking claims about Brit have already surfaced in excerpts - including that she watched their two sons sleep while holding a knife multiple times! Scary...