The history of filmmakers skewering Hollywood's darker excesses represents a long and rich one, from Billy Wilder through Robert Altman. With "Tropic Thunder," a rude, crude, over-the-top satire about rude, crude, over-the-top action movies, Ben Stiller makes an ambitious and surprisingly effective bid to join those vaunted ranks.

But let's be real: We're talking about a movie that gets its laughs from an improbably hilarious scene involving a severed head. The movie-within-the-movie, the eponymous "Tropic Thunder," is an adaptation of a Vietnam War memoir by Four Leaf Tayback (Nick Nolte). He's played by Tugg Speedman (Stiller), whose most critically acclaimed performance so far has been as a developmentally challenged farm boy in "Simple Jack."

Speedman's co-star is five-time Oscar winner Kirk Lazarus (Robert Downey Jr.) who has undergone a "pigmentation augmentation operation" to play his African American character. So Downey spends most of "Tropic Thunder" impersonating a racist jerk who spends the movie impersonating Redd Foxx. The actors, along with a supporting actor named Kevin Sandusky (Jay Baruchel) get dumped in the middle of the Southeast Asian jungle by their director (Steve Coogan, who's at the center of one of the movie's funniest scenes) to get more authentic performances.

Like in "Zoolander," Stiller puts his mouth into a petulant moue and paints dark rings around his eyes, the better to convey Speedman's elephantine ego. He and his pitch-perfect co-stars attack their roles with the gusto of gourmands tucking into a bacchanalian buffet.

"Tropic Thunder" has had its share of controversy, beginning with the decision to put Downey in "blackface" and for the film's use of the term "retard" to describe Speedman's "Simple Jack" character. But it's difficult to see the offense in either choice: Lazarus is repeatedly confronted by Alpa Chino (Brandon T. Jackson) for his insulting characterization of a black character, and a scene in which Lazarus criticizes Speedman for "going full retard" in "Simple Jack" is a put-down only of ambitious actors who take such roles because they're proven Oscar-bait.

With luck, that distinction won't prove too subtle for a movie whose modest ambition is nonetheless executed with giddy, boneheaded flair. -- Ann Hornaday (August 15, 2008)

Contains pervasive profanity including sexual references, violent content and drug material.