Many of those uses come in a scene where Downey, whose character Lazarus explains to Stiller's Speedman that his film "Simple Jack" bombed because he did the "full retard" as opposed to the "half retard" that Dustin Hoffman did in "Rain Man."
Tolleson says that, even in the context of the film, which is an "equal opportunity offender," he did not find the scene humorous. He added that there was no counter to the Simple Jack character as there was to Downey's character, who wears blackface throughout the film and is called on his stereotyping by a real black actor.
Despite, or perhaps in spite of, the screenings, an ad hoc coalition of more than a dozen disabilities groups held a conference call on the weekend to lay the groundwork for at least one protest in every state starting this week.
Film critic Peter Travers can understand how groups advocating for disabled people might be sensitive to their portrayal, but in this film, he said they are not the ones being spoofed. "It's egomaniac Hollywood actors, who know that, in order to please the Academy, they need to exaggerate every quality they can think of. It's a gigantic slap in the face, although a hysterical one, at Hollywood."
But Tolleson rejects the notion that disability advocates missed the joke. "We have a sense of humor," he said. "But just as it is with every other group, there are lines that shouldn't be crossed."
Shriver worries that viewers will see the film as an opening to humiliate and harass the intellectually challenged. Already, T-shirts that say "Don't Go Full Retard" are popping up for sale on the Web. Shriver said the studio has said it will pursue legal action to stop the sale.
Other films have mined people with disabilities for laughs, most notably the Farrelly brothers, who made "Something About Mary" and "The Ringer," in which "Jackass" star Johnny Knoxville pretends to be intellectually challenged so he can compete at the Special Olympics.
But Shriver, who was a consultant for "The Ringer," said that film tried to educate audiences "through humor about the giftedness of people with special needs." "Tropic Thunder," he said, "tries to humiliate actors by linking them to people with special needs."
One good thing that may come out of this film, Shriver believes, is the joining together of all these different disability groups for the first time. He believes this could represent a significant turning point in the fight for disability rights.
"Families have felt increasingly empowered and they have had enough," he said. "That hits square down the bull's-eye of this film coming out."
Tolleson added, "Rather than legislative change, we're talking about cultural change. That is harder. You can legislate changes, but until you make cultural changes, the job is not complete."
Associated Press contributed to this report