Stiller comedy skewers celebrities

Thanks to the American fascination with celebrity, every filmgoer can know more than he ever wondered about actors' preparation, Hollywood dealmaking and the extremes filmmakers reach to make movies.

We can debate whether that really improves anyone's enjoyment of movies. But it sure helps us enjoy "Tropic Thunder," an effective send-up of moviemaking that frolics in the hyperseriousness that surrounds big-budget flicks.

Ben Stiller co-writes, performs and directs, in the same spirit in which he confronted superfluous sports in "Dodgeball: A True Underdog Story," superheroes in "Mystery Men" and supermodels in "Zoolander."

Here, he places a squad of actors playing rescue-oriented heroes saving more heroes in Vietnam. When everything in the production goes haywire, the actors are left to their own devices, complicated by drug warlords with their own skewed brand of celebrity knowledge.

Most notable among the skewered targets is Robert Downey Jr., as Kirk Lazarus, a thinly disguised Russell Crowe who has undergone surgery to darken his skin so he may more authentically play an African-American sergeant. Downey overplays the role into submission.

Jack Black plays Jeff Portnoy, an actor breaking out of typecasting in inane, flatulence-dominated comedies (Eddie Murphy? Martin Lawrence?). Brandon T. Jackson plays a supposed female magnet calling himself Alpa Chino; Stiller himself plays fading leading man Tug Speedman. All boast quirks sufficiently obvious to link themselves humorously to well-known characters. A bonus product placement parody, set up by commercials delivered before the movie starts, works well, too.

Stiller isn't always as cute as he thinks he is -- especially when he tries sticking it to tired subjects like, say, agents (Lazarus' agent is played by Matthew McConaughey).

Similarly, Stiller's take on a studio boss, played by a bald Tom Cruise, is both over the top and mostly irrelevant. Cruise saves the moment by embracing the parody and pushing it wayyy past reasonableness.

Whether you get maximum impact may hinge on your appetite for celebrity trivia. (Even though advocates for the intellectually challenged are protesting Stiller's jokey take on actors playing the mentally disabled, they're probably missing the point.)

Even if you're full up to here with celebrity stupidity, you'll find Stiller's comedy to be anything but dumb.