Sometimes an Oscar nod is only an extra chromosome away. By playing mentally challenged characters, these actors stole suckers' hearts.

2. Sean Penn, <em>I Am Sam</em>- Sean Penn ranks as one of the greatest American actors of this era. He builds his characters from the inside out, imbuing them with deep humanity. He does not support the war in Iraq and often has polite disagreements with the paparazzi. Here, though…yeesh. It speaks volumes about how respected the guy is that he received an Oscar nod for this performance, in which he alternates between generic mentally deficient dad gestures (googly eyes at the daughter whose intelligence will soon trump his own) and performance art gone tragically astray (the anguished wail!).

1. Rosie O'Donnell, <em>Riding the Bus With My Sister</em>- The fixation on buying a toilet seat, the conspiracy theories about the moon, the Will Smith crush… Humankind may one day again approach the glorious apex of the unintentional comedy that was O'Donnell's performance as a junk-food-chomping, Chuck Taylor–wearing, public-transportation devotee, but we're not banking on it.

10. Cuba Gooding Jr., <em>Radio</em>- Forget the shameless based-on-a-true-story uplift and affirmation. Gooding's hammy performance as James Robert "Radio" Kennedy, who earned his nickname by swallowing whole a CD boom box (okay, not really), is all broad grins and dull plodding. It takes a lot to make viewers side with the bullies who pick on the mentally challenged dude, but Gooding somehow pulls it off.

9. Robert De Niro, <em>Stanley & Iris</em>- Technically, he's channeling a functionally illiterate here, not a mental simpleton. Nonetheless, De Niro plays it typically broad, dipping deep into his Master Thespian handbook (the downcast gaze, the pursed-lip pout) and rendering his character thoroughly schizophrenic. Separately: Being taught how to read by Jane Fonda is the cinematic equivalent of being taught how to aerobicize by Ayn Rand.

8. Billy Bob Thornton, <em>Sling Blade</em>- Sticking out one's lower lip and speaking in an English-as-a-second-language drawl makes a character appear more inbred than mentally deficient. Remember when the flick came out and corporate types adopted "French-fried 'taters" as their humor cornerstone, much as they did with Borat's "high five!" a few months back? Yeah, us, too. Sometimes freedom of speech really sucks ass.

7. Hank Harris, <em>Pumpkin</em>- You probably didn't see this movie, in which a moneyed sorority honey falls for a Special Olympics participant with angular cheekbones and wonderfully wispy hair. But if you did, you'd join with us in suggesting that the decision to cast a guy who looks like an Abercrombie & Fitch model in the part was not especially wise. Was Corky unavailable?

6. Jeremy Davies, <em>The Million Dollar Hotel</em>- Here's a handy 'tard-spotting tip for you: If a character is saddled with a name like Tom Tom, it's safe to assume that he's either a wee bit slow or a percussion instrument. Davies may have been trying to channel the unconflicted simpleness of Peter Sellers' character in Being There, but his village-idjit shtick plays like something out of a community-college drama class… A community-college drama class taught by Billy Crystal.

5. Ben Affleck, <em>Jersey Girl</em>- Wait—he wasn't playing a double-digit-IQ slug wit here? Who knew! In retrospect, this might have been his greatest on-screen moment.

4. Tom Hanks, <em>Forrest Gump</em>- Actually a fine performance from a comedic standpoint, especially when Tom/Forrest darts his eyes to and fro in the presence of luminaries like John Lennon. From a dramatic perspective, however, Forrest comes across less as an individual with a mental deficiency and more as a dumb-ass gas-station attendant from Alabama. Don't buy this? Take a ride down I-95.

3. Juliette Lewis, <em>The Other Sister</em>- The scene in which Lewis and Giovanni Ribisi, her fellow horndog halftard, page through The Kama Sutra together does more to trivialize the plight of these characters than anything short of outright, straightforward mockery. Lewis' lisp and mannerisms are broader and less sophisticated than anything you'd see in a typically cruel elementary school yard.