Downey: "Everybody knows you never do a full retard."
Stiller: "What do you mean?"
Downey: "Check it out. Dustin Hoffman, 'Rain Man,' look retarded, act retarded, not retarded. Count toothpicks to your cards. Autistic, sure. Not retarded. You know Tom Hanks, 'Forrest Gump.' Slow, yes. Retarded, maybe. Braces on his legs. But he charmed the pants off Nixon and won a ping-pong competition. That ain't retarded. You went full retard, man. Never go full retard."
When Tropic Thunder is stupid, it's a hilarious, farcical, deconstruction of the movie industry, and actors world wide. When Tropic Thunder goes completely stupid, it's just annoying. Unfortunately, it skews between the two often enough that it seems the film just isn't sure of what it wants to do.
The cast is star studded. Ben Stiller plays Tugg Speedman, an over the top action star on the downside of his career, similar to another actor on the film.