Hollywood execs say Katherine Heigl is 'difficult' and 'not worth' working with: Biggest celebrity brat?

Katherine Heigl has never thought of herself as America's sweetheart. And apparently, neither has anyone else.

According to an expose in The Hollywood Reporter, a handful of industry insiders all agree that the "Knocked Up" star is often too "difficult" to work with and ultimately, "not worth it." That's gotta hurt.

SODAHEAD SLIDESHOW: The biggest celebrity brats of all time

One insider elaborates on Heigl's alleged diva demands: "She can cost you time every single day of shooting... Wardrobe issues, not getting out of the trailer, questioning the script every single day. Even getting her deal closed at Warners was hard. She hit that point of 'no.'"

The article even makes the case that Heigl's difficulty has forced her off of Hollywood's "A list" -- making roughly $12 million on a given movie -- and back onto the small screen.

But is the former "Grey's Anatomy" actress the biggest celebrity brat you can think of? Surely, there's tons of divas in the industry. Kristen Stewart isn't exactly the sweet girl-next-door. Mariah Carey is often regarded in the industry as being a diva. And don't even get us started on Miley Cyrus.

From Katherine Heigl to Kristen Stewart to Miley Cyrus, who is the biggest celebrity brat of them all?