At decade’s end, “I Am Sam” will be in the 90th percentile of the worst of the worst. Only by virtue of its 1999 release does “The Other Sister” not get a similar designation for this decade.

At decade’s end, “I Am Sam” will be in the 90th percentile of the worst of the worst. Only by virtue of its 1999 release does “The Other Sister” not get a similar designation for this decade.

“Sam” and “Sister” feature characterizations of the mentally disabled so stereotypical they’re shameful. One of the worst bits of acting to get an Oscar nomination, Sean Penn’s “Sam” performance practically hinges on cute catchphrases. And in “Sister,” we’re asked to guffaw at the gaffes of Juliette Lewis and Giovanni Ribisi before feeling for their marital plight in the final act.

It’s performances such as these (specifically Penn’s) on which actor, co-writer and director Ben Stiller and company open fire in the film “Tropic Thunder,” which opened Wednesday.

Stiller plays Tugg Speedman, an actor rebounding from taking the title role in “Simple Jack,” a film about a mentally handicapped farmhand. Tugg thought it would get him an Oscar. It just got him reviled, as has “Tropic Thunder’s” use of the word “retard” in dialogue about the fictional role.

The Special Olympics, National Down Syndrome Congress and American Association of People with Disabilities have launched retaliatory protests. A promotional Web site for “Simple Jack” has been taken down. Timothy P. Shriver, Special Olympics chairman, told the New York Times he’s asking members of Congress for a resolution condemning what he called “hate speech” in the film.

Out of context, “retard” is harsh, hateful and taboo. In “Thunder” — spouted as it is by Hollywood idiots who confuse fidgety fingers and exaggerated laughter for humanity of the handicapped — it’s scathing satire at its finest.

Jack’s buckteeth and drawl aren’t Stiller’s way of mocking the disabled. It’s mocking the mentally incapable who can’t visualize or rationalize those with disabilities any other way. (Past Stiller collaborators the Farrelly Brothers are wonderful at warmly recognizing this within their own outrageous comedies like “The Ringer,” a film they produced and the Special Olympics vetted.)

Boycotting is well within these groups’ rights, but “Tropic Thunder” simply isn’t the film they should protest — it’s those that offensively settle for oversimplification instead of complex characterization.

Nick Rogers can be reached at (217) 788-1515 or nick.rogers@sj-r.com. Read his blog at blogs.sj-r.com/unpaintedhuffhines.