By RICK EGUSQUIZA

Kirstie Alley may have lost 60 pounds, but she's gained a ton of bad attitude!

The Fat Actress star's been angering co-workers on the set of her new Jenny Craig commercials because the pressure of losing weight has finally gotten to her, say insiders.

"Kirstie looks terrific on the outside — but these days she's a complete bear to work with," a close source told The ENQUIRER.

"When Kirstie was fullfigured, she was easy to work with. Completely trouble-free. A dream. But now that she's focused on weight loss, she's turned into a real nightmare."

Pick up The ENQUIRER for more on details!