Betty White’s a potty mouth. The squeaky-clean actress — best known to TV audiences as the two-faced happy homemaker Sue Ann Nivens on “Mary Tyler Moore” and the ditsy Rose on “The Golden Girls” — plays a foul-mouthed, batty old woman in David E. Kelly’s “Lake Placid,” a new movie about a man-eating crocodile. White plays Delores Bickerman, who doesn’t report that a 30-foot crocodile ate her husband because she doesn’t want anyone to kill the poor beast. White, a real-life animal-rights advocate, is oh-so-sorry about the language. “(David) said, ‘I’m not sure the crocodile stuff will work, but to hear that language come out of Betty White just cracked me up,'” she recalled.