BROTHER FROM ANOTHER MOTHER: Ben Stiller and Robert Downey Jr. in Tropic Thunder.

At the climax of the Hollywood-gone-upcountry spoof Tropic Thunder, after action hero Tugg Speedman (Ben Stiller) and a troupe of entitled actors have accidentally wandered into a Laotian drug ring while trying to wrap a Vietnam movie, Speedman rushes back into enemy territory for a moment of personal redemption. “Tell the world what happened here,” he charges his colleague Kirk Lazarus (Robert Downey Jr.). Lazarus agrees, but first he wants to clarify one point: “What happened here?”

Damned if I know. One thing’s for sure: Some $90 million of Paramount Pictures’ money was spent on a bloated dud of a comedy. As the director of The Cable Guy and Zoolander, Ben Stiller has favored the kitchen-sink approach—throw everything at the screen and see what sticks. In Tropic Thunder, that method mostly means trying to have it both ways. Stiller has made a cheekily gory movie in which little of the violence has any lasting impact. (In one representative joke, a small child is tossed fiercely off a bridge, only to emerge unharmed moments later.) He mocks bloated-budget spectacles while filming his own combat scenes with glossy self-admiration. He, Jack Black and Tom Cruise all play parodies of recognizable Hollywood types—the lunkhead, the coke fiend and the unscrupulous executive—but who exactly is Tom Cruise in the position to lampoon? This is a satire of movie-industry excess constructed by the very people made fat and happy by that industry. It has plenty of explosions, but it lacks the animating fire of hatred.

The only jokes that land are the ones you’ve already heard about, the ones that needle taboos. Disability-rights groups are promising to picket Tropic Thunder for sneering at movies about “retards,” but where are they when the real-life counterparts of Tugg Speedman (Sean Penn, Cuba Gooding Jr.) make the real-life equivalents to Simple Jack (I Am Sam, Radio)—cynical pictures about the uplifting power of the mentally handicapped? The activists should be smart enough to see the joke isn’t directed at them.

Then there’s Downey as Kirk Lazarus, the Australian actor so dedicated to winning Oscars (previously starring as a gay monk opposite Tobey Maguire in Satan’s Alley) that he gets his skin pigmentation ratcheted up several shades and starts talking in a gruff bark that lands somewhere between the two Shafts—Richard Roundtree and Samuel L. Jackson. The gag again lacks a sure target—blackface is not, in fact, a sure route to awards, unless Downey wins some here—but the actor attacks his character-within-a-character with a bizarre conviction. Downey has always seemed to be operating on a plane separate from his fellow performers, and here he skewers his own detachment, boldly blazing a trail through the jungle that only Kirk Lazarus can see (it has something to do with The Jeffersons, and crawdads). Nobody else in Tropic Thunder has his certainty. As Lazarus explains it: “I’m the dude that’s playing the dude disguised as another dude. You’re the dude that doesn’t know which dude he is.” Exactly. R.