Life as Justin Timberlake must be pretty rough. He has Cameron Diaz as a GF, and now, he gets to film sexy scenes with Scarlett Johansson for his new music video, "What Goes Around." But insiders for Ted Casablanca's The Awful Truth report that Justin and his co-star were pretty rough to work with on the set.

For starters, instead of signing a confidentiality agreement (totally normal), workers on set had to sign letters to "Mr. Timberlake" vowing not to reveal deets about the shoot (not normal). Well, it seems like someone did spill, and now we see why JT was so secretive about the shoot -- he and Scarlett are nutso!

On the set, JT allegedly wouldn't let anyone make eye contact with him. "When they were setting up for the shot, Scarlett's stand-in accidentally caught [Justin's] eye," a source tells The Awful Truth. "He moved his chair out of her line of sight after that."

As for Scarlett, she complained about not being able to smoke on set. (We know how she loves her smokes -- gross!) "How come we have fire dancers, but I can't smoke?" she whined. And while she wanted to inflict secondhand smoke on everyone, she wouldn't let people even eat near her. When a few crewmembers went outside to eat, Scar was in the nearby vicinity. "She had her bodyguard come over and tell them they couldn't eat around her," the source says.

Sounds like two people forgot to take their crazy pills that morning...