Alpa Chino (BRANDON T. JACKSON) is a popular hip-hop performer who has a growing product franchise and is expanding his empire into the movie business. And then there's award-winning Australian actor Kirk Lazarus (ROBERT DOWNEY JR.) who's so dedicated to his art that he immerses himself completely in whatever role he's playing, such as surgically changing his skin pigmentation to play an African American.

They're joined by rookie actor Kevin Sandusky (JAY BARUCHEL) on the set of "Tropic Thunder," a big-budget Vietnam war pic about the story of legendary Sgt. Four Leaf Tayback (NICK NOLTE), who's now on the set as an advisor to Damien Cockburn (STEVE COOGAN). He's the director who's in over his head, what with the demanding and/or troubled actors, trigger-happy explosives coordinator Cody (DANNY McBRIDE), and an angry Hollywood mogul, Lee Grossman (TOM CRUISE), and his subordinate studio exec, Rob Slolom (BILL HADER).

Four Leaf realizes what's wrong with the production -- a lack of authenticity -- and thus encourages Damien to place his actors in country so that they can experience something close to the real thing. With Cody providing the explosives and told that there are cameras everywhere to capture their scene acting, the performers go about performing their roles. While Tugg's agent, Rick Peck (MATTHEW McCONAUGHEY), is concerned about his client's lack of a digital video recorder on location, the actors don't realize they've landed in the midst of drug fields of the Flaming Dragons led by the young Tran (BRANDON SOO HOO).

Of course, they think the armed rebels are just part of the film, but are on their own when Damien takes a wrong step. From that point on, it takes a while before they eventually realize their private little movie war has turned into something completely different.

Nowadays, minority entertainers can portray white folk (see any number of Eddie Murphy characters or films such as "White Chicks"), but it's considered a risky move -- some may even say professional suicide -- for the reverse to happen. Michael Richard's post-"Seinfeld" public comments apparently reveal why he might not have had a hard time doing several mock versions of that on the famous sitcom, but that's chump change compared to what Robert Downey Jr. attempts to pull off in "Tropic Thunder."

You see, the talented American actor plays an Aussie star (think Russell Crowe) who decides to go one better than donning makeup to play a black character in his upcoming war flick -- he surgically changes his appearance to that of an African American.

Now before Jesse Jackson and Al Sharpton get all worked up into a racial tizzy, they (and everyone else) must remember the cardinal rule of portraying an ethnic group that isn't naturally your own. Namely, that it's fair game as long as any goofy or related material makes fun of the person in the makeup and not the group they're representing.

That's certainly the case in this comedy from Ben Stiller (director, co-writer, co-producer and co-star) that takes politically incorrectness to new heights -- or lows depending on how one might view such material. Downey Jr.'s is just one part of this uneven but sometimes outrageous, belly-laugh funny flick, but it's clearly the juiciest and the most fun. With the film -- also penned by Justin Theroux -- being about the making of a film of the same title set in Vietnam, Mr. Iron Man himself plays a method actor so dedicated/immersed in/obsessed with his work that he never falls out of character, even when the cameras aren't rolling.

And that's of a Vietnam era black American soldier as commonly found in the movies of that time. It's a delicious bit of satire about such performers and the industry that feeds them, not to mention those cinematic characterizations, and the actor is once again clearly on the money, proving he's one of the most versatile guys in the biz at the moment (although it's uncertain what Crowe might think of such mockery).

Stiller and company don't stop there, however, as all sorts of Hollywood machinery is directly in their targets, from the obvious war movie material (any number of such films and genre clichés are pegged) to looney media moguls (an initially nearly unrecognizable Tom Cruise really sinks his teeth, not to mention four-letter word vocabulary into the part).

Then there are the desperate talent agents (Matthew McConaughey keeping his buff bod under wraps for once, sorry ladies), drugged out stars (a blonde Jack Black), Eddie Murphy/Martin Lawrence type multiple role movies featuring farting (Black again), hip-hop entertainers (Brandon T. Jackson playing an amusingly named Alpa Chino), in-over-their-head directors (Steve Coogan who exits in a gruesomely funny way) and so much more.

Not all of it hits with the sort of consistent razor sharp accuracy one would like to see in a flick like this, some of it's likely too graphic for some viewers (including some over-the-top war wounds), and others may take offense at any number of topics where tip-toeing is obviously frowned upon. That includes a spot-on discussion between Downey Jr. and Stiller's characters about the latter wrongly choosing to "go full retard" in portraying the title character in "Simple Jack," a "Forrest Gump" sort of rip-off.

Things get off to a bang -- literally and figuratively -- with a faux movie theater ad and three trailers for upcoming releases (that are fun in their send-up of the real thing, likely inspired by Quentin Tarantino doing something similar during his double-feature with Robert Rodriguez last year), followed by an opening war scene that not surprisingly pulls back to reveal it's just the making of a scene of the movie within the movie.

Granted, pics that bite the industry hand that feeds them aren't a dime a dozen, but they're also not so unusual that this is any sort of novel idea. The same holds true for blackened comedy and politically incorrect material, the kind of which often teeters along a fine line between funny and misfire.

Yet, Stiller and his merry band of parody players get more than just enough of it right (especially regarding Downey Jr. who could receive some award accolades down the pike for his brilliant send-up), and elicit some of if not the biggest laughs of the year that the film earns a recommendation for adults who don't mind the profane and irreverent material. "Tropic Thunder" rates as a 6.5 out of 10.