Batman movie “The Dark Knight” has been a box office behemoth with four straight weekends atop ticket sales charts, but some industry watchers expect the new comedy adventure “Tropic Thunder“ could knock it off its No. 1 perch this weekend.

“Tropic Thunder,” which stars Ben Stiller, Jack Black and Robert Downey, Jr., opened in theaters on Wednesday with a healthy $6.5 million for the one night, slightly above expectations, said the DreamWorks movie studio which is behind the movie.
    
That was about half the $12.15 million first-day total of stoner comedy “Pineapple Express” last Wednesday, and ”Express” failed to beat ”Dark Knight” this past weekend when ticket sales were tallied. “Express” had $23 million for the weekend to $26 million for “Dark Knight.”

With a 44 percent drop – which is the average decline over the past few weeks for “Dark Knight” – it should have weekend ticket sales in the mid-teens, which is below the $20 million that DreamWorks expects from “Tropic Thunder” this weekend.
    
“Friday and Saturday I think are going to be big days for (”Tropic Thunder”), and it may have a shot at knocking out ‘Dark Knight’ from number one,” said Paul Dergarabedian, head of box office tracker Media By Numbers.
    
As of Wednesday, “The Dark Knight” had taken in nearly $452 million in the United States and Canada, according to the Web site for Box Office Mojo. It has ruled the box office every weekend since it opened on July 18. 

As an R-rated movie, “Tropic Thunder” has been difficult to advertise on TV because the most outrageous parts of the movie cannot be shown to all audiences. DreamWorks hopes the midweek opening can help overcome that difficulty.
    
“The great word of mouth from the Wednesday and Thursday opening will push people to see the movie this weekend,” said Chip Sullivan, a spokesman for DreamWorks.

Hollywood has long been populated by egocentric actors, actresses, directors, writers, producers and other narcissists who are easy to poke fun at. This week “Tropic Thunder,” directed by Ben Stiller and starring him, Jack Black and Robert Downey, Jr., is the latest film to take a satirical look at high-profile stars. But is there any joke that goes too far when Hollywood insiders are making fun of Hollywood?

Not really, said Justin Theroux, a co-writer with Stiller on the movie. ”The good thing about Hollywood is that I don’t think you’d be able to show this to anyone and have them go, ‘God that’s so me,’ They’ll all go, ‘That’s that guy,’” Theroux, 37, told reporters in recent interviews.

“Tropic Thunder” is about a group of actors making a war movie. Shooting goes haywire and the leading man is kidnapped by drug dealers, forcing the other actors to overcome their personal hang-ups as they rescue their co-star. 

Stiller, 42, told reporters the idea for the film came from seeing actors attend boot camp before appearing in war movies then hearing them talk about how it was a life-changing experience, which Stiller said confounded him.
    
The movie’s main characters are based on Hollywood archetypes, such as the Oscar-winning actor (Robert Downey, Jr.), the fat comedian (Jack Black) and the hip-hop artist (Brandon T. Jackson) trying to make it as an actor. Stiller plays a movie action hero.
    
In the case of that last character — the hip-hop artist – the character is named Alpa Chino, which of course sounds like Al Pacino. Stiller said he told the acclaimed actor that he would have a namesake of sorts in “Tropic Thunder.” Pacino was tickled, Stiller said.
    
Theroux said writing the script was harder when the movie was just a concept years ago, because the average movie fan’s knowledge of Hollywood’s inner workings was not as advanced back then. With the advent of the celebrity Web site TMZ.com and other Hollywood news on the Internet, that is no longer a problem, Theroux said. 

“The knowledge of what goes on behind Hollywood now has sort of caught up with our script, weirdly,” he said.
    
(Reporting by Alex Dobuzinskis)  

Having a behind-the-scenes celebrity mom isn’t something Paris Hilton or her sister Nicky would know much about. Their mom, Kathy, seems to relish the  spotlight as much as her girls.

Having recently launched her own perfume and starred in a Web mini-series called “A Day With the Hiltons,” the 49-year-old Kathy Hilton has now nudged her way into Hollywood movies with a cameo appearance in Ben Stiller’s new summer comedy “Tropic Thunder,” playing Tom Cruise’s wife, according to In Touch Weekly.  

“She filmed last winter and didn’t even tell her kids because she wanted to surprise them,” a set insider told the celebrity magazine. “She raved about Tom,” said the insider. 

After filming “Tropic Thunder,” Kathy Hilton also shot a few episodes of daytime TV soap opera, “The Young and The Restless.” The older Hilton has been a sometime actress for years but not winning the same success as her girls. A reality TV show she hosted in 2005 called “I Want To Be A Hilton” flopped.