Robert Downey Jr. was very reluctant to take the role because he felt wearing the make-up to look African-American was offensive. But Downey later accepted the role because he liked the script and wanted to work with Ben Stiller and Jack Black.
Like his character, Kirk Lazarus, Robert Downey Jr. is a method actor and stayed in character as Sgt. Osiris/Lazarus even while cameras weren't rolling.
As part of a promotional tie-in, the 'Booty Sweat' energy drink seen in the movie was available for a limited time on Amazon.
For the fake trailer, "Satan's Alley", Tobey Maguire came in at the very last minute to film the role of Robert Downey Jr.'s monk lover. He did it as a personal favor for Ben Stiller and Wonder Boys (2000) co-star Downey.
Owen Wilson was originally set to play Rick Peck, but after his attempted suicide, Ben Stiller gave the role to Matthew McConaughey.
Ben Stiller says that nearly all aspects of the Les Grossman character were developed by Tom Cruise, including the dancing and the look of the makeup. Stiller said that in addition to the more obvious makeup effects applied to Cruise's face and head, and the extra hair on his chest and arms, Cruise also decided to play the character wearing over-sized prosthetic hands.
It was said by Jack Black himself, he declined his role in Tropic Thunder due to the fact he would have to color his hair blonde. He soon changed his mind but was not too pleased.
The water buffalo that Jack Black's character rides was discovered to have been pregnant when the cast and crew came back to the set one morning and found her nursing a newborn calf.
For all the violent action in the plot, the only deaths depicted in the movie are of director Damien Cockburn and the panda bear.
In the film, Kirk Lazarus says "I don't drop character 'til I've done the DVD commentary." When recording the audio commentary for the unrated DVD and blu-ray, Robert Downey Jr. actually spends the entire commentary in the character that appears on the screen as the movie progresses.
So long, and thanks for all the fish!