The comedy in "Tropic Thunder" is as sophisticated as a whoopie cushion.

And that's good thing.

But wait, there's more. The film is also consistently offensive, frequently disgusting and politically incorrect to the max. More importantly, it's hysterically funny, that is if you like your humor swirling around in the gutter.

That said, this movie has something most of the other lowbrow comedies released this year lack - a bit of smarts. It also features performances far more inspired than you'll find in a typical film of this ilk.

Described as an action comedy, "Tropic Thunder" spends most of its time spoofing the action genre in general and self-absorbed, pampered actors in particular. It also takes cannon-sized shots at agents, directors, special effects coordinators, authors and studio bosses.

The film generates laughs immediately with a fake commercial for Booty Sweat and Bust-A-Nut, products you probably won't find at Whole Foods, followed by fake trailers for films starring clueless action superstar Tugg Speedman (Ben Stiller), drug-addicted, gross-out comedian Jeff Portnoy (Jack Black) and Australian method actor extraordinaire Kirk Lazarus (Robert Downey Jr.).

In this film-within-a-film, satire abounds with Stiller's Speedman parodying all manner of action stars, especially Sylvester Stallone's Rambo. Black's Portnoy mocks actors who play multiple roles requiring fat suits and plenty of flatulence, much like Eddie Murphy in "The Nutty Professor" films. Downey's Lazarus ridicules method actors who remain in character throughout a film's shooting schedule, much like Daniel Day-Lewis in any of his movies.

All three prima donnas star in "Tropic Thunder," a Vietnam War movie being shot on location (Hawaii in reality) under the direction of flustered first-timer Damien Cockburn (Steve Coogan). "Platoon" and "Apocalypse Now" get skewered here. As the stars bicker over such critical topics as crying jags, the film spirals out of control. It's way over budget and the studio boss, Lee Grossman (an almost unrecognizable Tom Cruise), is not pleased. He orders a key grip to punch out Damien. Outrageously profane and displaying all the morals of a pit viper, Grossman, as portrayed by Cruise, is worth the price of admission alone. Any similarities between Grossman and former Miramax chief Harvey Weinstein are purely coincidental.

To try to inject some realism into the film, John "Four Leaf" Tayback (Nick Nolte), a grizzled veteran who wrote the book upon which the film is based, convinces Damien to send the stars deep into the jungle. There, special effects guru Cody (Danny McBride) has set up explosive devices at strategic points.

The actors agree, but the shoot goes terribly awry when real drug dealers show up and mistake the thespians for drug agents. Lazarus realizes what's going on, but Speedman believes the dealers are simply actors and blindly forges ahead. The results are not pretty, but they sure are funny.

Downey, who was amazing as the titular superhero in "Iron Man" earlier this year, can add another fabulous performance to his resume thanks to "Thunder." To play his role as an African-American, Lazarus goes Mount Everest over the top. He has his skin surgically dyed black and speaks with a "black" accent. His blackface routine, which he continues even when the film gets sidetracked, seriously irritates a real black actor, Alpa Chino (Brandon T. Jackson). Yes, say the character's name again for the joke. Also going along for the bumpy ride is the film's rookie actor Kevin Sandusky (Jay Baruchel). Matthew McConaughey, meanwhile, plays Speedman's TiVo-touting agent in a role reportedly intended for Owen Wilson. McConaughey apparently stepped in after Wilson's suicide attempt.

In one of the film's many insensitive yet insightful scenes, Lazarus critiques Speedman's performance as a mentally challenged man in "Simple Jack." Think Sean Penn in "I Am Sam." The language used here should offend virtually everyone. To add insult to injury, "Simple Jack" turns out to be the drug lord's favorite film and he orders Speedman to re-enact the role.

Though Downey's performance dominates the proceedings, Cruise nearly steals the film as Grossman. The actor, better known for his dramatic roles, proves in "Thunder" he can do comedy, too. And dance.

While "Tropic Thunder" lags in parts and some jokes hit the funny bone harder than others, the film represents a quantum leap in quality from Stiller's previous film, "The Heartbreak Kid." Interestingly, that movie was made by the Farrelly brothers, who directed Stiller in his first big hit, "There's Something About Mary." Stiller, as director and co-writer of "Tropic Thunder," clearly demonstrates he learned a thing or two about grossness and politically incorrectness from the Farrellys. And that's a good thing.

"Tropic Thunder" opened Wednesday, Aug. 13, 2008.

"Tropic Thunder"

Starring Ben Stiller, Jack Black and Robert Downey Jr.

Rated R (for pervasive vulgarity, sexual references, violent content and drug material), 106 minutes

Directed, co-produced and co-written by Ben Stiller