In Rolling Stone's new Britney Spears cover story, Spears reveals that she thinks her ex-husband Kevin Federline is letting the kids pick up some bad habits. "Preston says the f-word now sometimes," she says. "He doesn't get it from us. He must get it from his daddy." She talks more about her relationship with K-Fed ("I think I married for the wrong reasons") in the documentary Britney: For the Record, which airs on MTV November 30th at 10 p.m. Click above to watch Spears get introspective about her marriage.