Is Brittany Murphy totally "clueless" about appropriate on-set behavior? Sources on the set of her new movie, Across the Hall, think so, saying that Brittany's been acting "like a diva," Page Six reports. "She's extremely difficult," an insider says. "When she gets to the set, it comes to a grinding halt. She's so hot and cold, you never know."

Among her crazy demands is insisting on having her PB&J sandwiches cut diagonally with the crusts removed. "She needs one every hour. It's painstaking -- her assistant takes about a half an hour making each one," a crewmember says. Plus, Brittany's hubby has been interfering with filming so much that the movie's producers had to meet to discuss how to deal with him! Sounds like she's as much of a hassle to deal with as another Britney we know…