Opposites do more than attract in Ben Stiller's unapologetic R-rated comedy "Tropic Thunder" - they loudly and defiantly collide.

Simultaneously smart and dumb, mixing clever satire with way over-the-top raunch and unrelenting profanity, this equal opportunity offender risks running off some of the very people who might appreciate it the most.

In his first turn at starring, directing and cowriting since 2001's memorable "Zoolander," Stiller has taken as his target all things Hollywood, including the perfidy of producers and agents, and the self-involvement of actors who say things like "I don't read the script; the script reads me."

But because the world of contemporary show business, from the bloodletting of the slasher franchises to Britney Spears without underwear, is often so extreme, parody necessitates being even more excessive, leading in this case to a severed head and blood that spurts like Old Faithful as well as language and situations that give new meaning and dimension to the notion of going too far.

Not only is "Tropic Thunder" guaranteed to offend, it already has. One of the mock films it references, "Simple Jack," and its story of a developmentally challenged young person who talks to animals, uses the tagline "Once upon a time ... there was a retard." This has so upset advocacy groups that news reports say a coalition of them is intending to call for a nationwide boycott to protest "the movie's open ridicule of the intellectually disabled."

But it would be regrettable if "Tropic Thunder's" undeniable excesses, including having an actor indulge in the 21st century version of blackface, blinded viewers to the reality that, like it or not, there is genuine humor and palpable satiric intent underneath the waves of unnerving bad taste and political incorrectness. That comes not only from the script but from the film's committed and very funny actors, whose characters are presented in an especially clever way.

Because "Tropic Thunder" is the story of a group of thespians who come together to star in a Vietnam War action movie, Stiller chooses to introduce them with mock trailers from their last films, or, in the case of hip-hop star turned actor Alpa Chino (comic Brandon T. Jackson), with a salacious theatrical ad for his hot new energy drink, Booty Sweat.

As these trailers remind us, Stiller has a gift for take-no-prisoners sketch humor that goes back to his short-lived, Emmy-winning TV series "The Ben Stiller Show." Although it certainly has a plot, "Tropic Thunder" is best approached as a series of skits stretched out to feature length, a film easier to appreciate for its clever parts than for any kind of coherent whole.

Four actors (played by Jackson, Stiller, Robert Downey Jr. and Jack Black), along with boyish newcomer Kevin Sandusky (Jay Baruchel), have gone on location in Vietnam to film the heroic memoirs of John "Four Leaf" Tayback, a gnarled veteran with prosthetic hands and a brooding presence (who else but Nick Nolte).

When director Damien Cockburn (Steve Coogan) starts to lose control of his high-powered actors, it's Four Leaf who suggests taking them out to the jungle and shooting the whole movie guerrilla-style until, in the director's memorable words, "you'll be begging for a body bag if it means a ride home."

Lurking in that jungle, unfortunately, is a Vietnamese heroin-producing plant run by the dread Flaming Dragon organization, and that reality ends up changing everything for the cast and its Hollywood support teams.

Like the actors stranded in the jungle, patrons of "Tropic Thunder" have to be ready for anything thrown at them by a film with a sensibility that makes the Three Stooges look like Faith, Hope and Charity. That includes a memorable conversation between a downcast Tugg Speedman and Kirk Lazarus, determined to stay in character and keep his ghetto mannerisms until after the DVD commentary is recorded, about the pitfalls of an actor going "full retard" in search of an Oscar nomination.

It would be easier all around, obviously, if we lived in a culture where the potentially offensive and the undeniably comedic weren't linked as closely as they are, but contemporary moviegoers don't have that choice. You pays your money and you takes your chances. It's as simple, and as complex, as that.