when an actor portrays a mentally disabled character as *totally* mentally disabled, with few if no redeeming values. Oftentimes in Hollywood, actors are known to sink to the lowest common denominator, and try to play mentally disabled characters in what are really shameless attempts to win audience and critic sympathy, in what is usually a desperate bid for an Oscar. Sometimes, playing a mentally disabled character actually *does* result in winning an Academy Award, so long as you *don't* "go full retard":
That is, the mentally disabled character *should* face some obstacles, but also have some redeeming values (an "idiot savant"). For example, Dustin Hoffman in "Rain Man" was "mentally disabled" but he was really an autistic mathematical genius. Tom Hanks in "Forrest Gump" was mentally handicapped, but it still a very functional individual and in his own way, charming in his honest if simple morality to people me meets, and further, he has some real above-average talents, such as being an Olympic-level ping pong player and an excellent long-distance runner.
However, this doesn't work if the actor's performance as the mentally disabled character has *absolutely* no redeeming values and is indeed "full retard" mode: a character that is utterly handicapped mentally and really has no "hidden surprise talents"; this ends up just being a film following an average mentally disabled person around for the whole run time.
Such was infamously the case with Tugg Speedman's flop movie "Simple Jack". That is not to say that Speedman gave a lazy performance: on the contrary, he spent untold hours studying mentally disabled people until he could perfectly imitate what such a person would act and sound like.
The problem is...that's not what Oscar-voters want to see. They don't want to see the struggles of a mentally disabled person in everyday life. What gets the Oscar votes in such performances are unrealistic "idiot-savants" who while mentally handicapped, might be really good at mathematics, or a good painter, etc. etc.
In and of itself, this means that ironically, Hollywood isn't actually interested in films about what real mentally handicapped people are like; they're interested in movies about characters who have a few mental handicaps, but are also capable of unrealistically extraordinary things.
What Speedman did, actually trying to portray a character as *fully* mentally handicapped without any "hidden talents", is a death sentence for a film.
This is why actors in films that actually portray what real-life mentally handicapped people are like, such as Cuba Gooding Jr in "Radio", or Sean Penn in "I Am Sam", have failed to win Oscars for their performances.
In short, an actor should never "go full retard" if they expect to make a successful Oscar vehicle.
"Check it out. Dustin Hoffman, Rain Man. Looked Retarded. Acted Retarded. NOT retarded. He could count toothpicks, cheat at cards. Autistic. Sure. NOT retarded. Tom Hanks' Forest 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! Peter Sellers, "Being There", infantile? Yes. Retarded? No.
You went full retarded man. You never go full retard.
Don't believe me? Ask Sean Penn, 2001, I am Sam. Went full retard. Went home empty handed."