A band of brothers explodes in spoofy sibling revelry

Jokes within jokes. Movies within movies. A reel suicide mission that turns into a real one.

Ben Stiller's Tropic Thunder is raunchy, raucous and riotously funny. But so acutely self-conscious that the effect is one of a stand-up comedian furnishing color commentary on his own act.

Written by Stiller, Justin Theroux and Etan Cohen, the movie about the making of a Vietnam War movie called Tropic Thunder is a self-mocking comedy tweaking showbiz self-importance. And an action flick chronicling a studio's bungle in the jungle. And an excessive inventory of Hollywood excesses.

On the desert-island location of Tropic Thunder, a milquetoast director (Steve Coogan) endeavors to film the muscular memoir of a macho paraplegic (Nick Nolte). The filmmaker is saddled with wimpy actors who go together about as well as chalk and chowder.

In general, they represent the band-of-brothers population of war movies. In particular, types that appeal to reliable moviegoing demographics, the action guy with the bulging biceps, the serious actor with the bulging cranium, and the hip-hop impresario with the bulging pockets.

Action lug Tugg Speedman (Stiller) is a Stallone-esque grunter in a sweatband, out to redeem his career.

Speedman's one-note emoting appalls thespian Kirk Lazarus (Robert Downey Jr.), a Russell Crowe-like Aussie perfectionist who resorts to "pigment augmentation" (read: blackface) to play an African American.

Lazarus' hubris appalls African American entrepreneur Alpa Chino (Brandon T. Jackson), a P. Diddy-like businessman who views acting in movies as an extension of the brand.

Then there are the druggie (Jack Black as Eddie Murphy-ish comic Jeff Portnoy, eager for dramatic cred) and the male ingenue (Jay Baruchel as Kevin Sandusky, eager to survive), respectively out of it and new to it. Kevin is appalled that seasoned filmmakers and actors can't tell the difference between prop grenades and the type that sever limbs.

Like the explosives detonated by Tropic Thunder's overzealous technician (Danny McBride), Stiller's film carpet-bombs for laughs when it would be more joke-effective to go for the surgical strike. While aiming for the funnybone, the filmmakers bruise other body parts.

Three performances survive the bombs and the blood and the viscera, two of them cameos.

As Tugg's agent, Rick Peck, a role originally written for Owen Wilson, the uncredited Matthew McConaughey is hilarious playing a guy in the Hollywood bubble that bursts when he learns that his client is in mortal danger.

Wearing fatsuit and bald cap, unrecognizable in the role of the film's vulgarian producer, Les Grossman, Tom Cruise, as his character's name suggests, cares more about grosses than human lives.

Best of all is Downey, whose rumbling dialogue has the wah-wah sound of an R&B guitar and the authority of the late Isaac Hayes. As usual, Downey is sublime, lightly funny in a screenplay where the humor is often heavy-handed.

Stiller is more effective behind the camera than on screen as Tugg, a role reportedly written for Keanu Reeves. Tugg spends the movie trying to live down the ignominy of having played a Forrest Gump-like character in a box-office failure.

Are the film's caricatures insulting or offensive to African Americans and the mentally disabled? As its targets are not blacks or the mentally disadvantaged but actors who would do anything for awards, I think not. (That said, the film's depiction of cartoony Asian druglords did seem like an anachronism from 1940s war films.)

With its repetitious passages of stumble-in-the-jungle slapstick and geysers of in-jokes, Tropic Thunder finally is more successful as a critique of Hollywood movies than as a Hollywood comedy.

But it has just enough surprise laughs to guarantee a freak meteorological event. This Thunder will precede box-office lightning.