Director Raja Gosnell (Never Been Kissed) struggles to combine gross-out comedy, saccharine drama, and looming danger as a bank robber who’s escaped from prison hunts for his ex-girlfriend and her son. They’ve left their home to make peace with a distant relative so they’ll have somewhere safe to stay, but they don’t know that an FBI agent (Martin Lawrence) is impersonating the relative, a woman much fatter and older than he is. Though the real Big Momma (Ella Mitchell) in this neither good nor terrible movie is rude and dismissive, the agent portrays her as sweet and understanding; his impersonation “fools” the people who know her mainly because they like him better. When he isn’t dressed as a woman, Lawrence poses as a handyman and courts the robber’s ex-girlfriend, hoping she’ll confide in and fall in love with at least one of his identities; he brings to his nested role a disarming sincerity that somehow prevents all the erection jokes and more serious declarations of affection from canceling one another out. Darryl Quarles and Don Rhymer wrote the screenplay; with Nia Long, Terrence Howard, Jascha Washington, and Paul Giamatti. 99 min.