"Tropic Thunder" is a thunderous bore. And that's despite stuff blowing up all over the place and the manic antics of Ben Stiller, Robert Downey Jr. and particularly Jack Black.

This indulgent film is about a bunch of pampered actors who've come together to make a "Rambo"-like picture set during the Vietnam War. For realism, there are choppers and blood and limbs torn off.

When the intimidated director (underutilized Steve Coogan) can't get the lazy cast to cooperate and a multimillion-dollar explosion shot is wrecked (the cameras weren't rolling), he takes them deep into the Southeast Asian jungle for real.

But once there, the picture evolves into a gruelingly unfunny escapade in which Stiller gets captured, tortured and forced to perform the role that nearly ruined his career in a movie called "Simple Jack" — a mentally handicapped man with buck teeth.

Earlier, Downey's Kirk Lazarus tells him the film wasn't well-received because it was played "full retard. You can't go all the way retard." Then, as examples, he uses Dustin Hoffman in "Rain Man" and Tom Hanks in "Forrest Gump." It's scurrilous.

Downey, meanwhile, portrays a black man (with bleached skin) to the stereotypical hilt. There's the "N" word and a discussion of the phrase, "You people." The lone African-American in the film-within-a-film's cast (Brandon T. Jackson) tells him, "Cool it, Benson."

In one scene, Stiller, dying on the battlefield, recites, "I can't feel my legs." Responds Downey, in dialect, "Ain't nothin' but a thang." Downey knows what he's doing and you can appreciate the actor's effort, misguided as it is.

Stiller directed, co-produced and co-wrote the film, and he accomplishes something seemingly impossible — turning Black into a human being not only vulgar but also grossly unfunny. The likable actor from "School of Rock" and "Nacho Libre" is burdened with an abundance of fat and flatulence jokes. It's a sad display.

There is one memorable performance. Tom Cruise goes nuts as a bald, crass, over-the-top Hollywood tyrant, cussing multiple variations of a certain four-letter word. And he likes to dance by himself to hip-hop music. It's a great incarnation.

When Danny R. McBride (from the superior "Pineapple Express") as a special-effects guru, says, "I almost blinded Jamie Lee Curtis on `Freaky Friday,'" the line didn't play.

At one point, Downey's taken-with-himself actor intones, "I don't read the script. The script reads me." He should've read the script to "Tropic Thunder."

"Tropic Thunder" Rated: R. Running time: 1 hour, 46 minutes. 1 1/2 stars.

To find out more about Lee Grant and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

COPYRIGHT 2008 CREATORS SYNDICATE INC.