BEVERLY HILLS -- If playing inglorious bastards was an art form, then Billy Bob Thornton would be its Picasso. The 51-year-old actor once again picked up nefarious oils and painted with broad strokes in "Old School" director Todd Phillips' "School for Scoundrels" as Dr. P, a mischievous teacher who is more scallywag than Socrates.

In the film, Dr. P runs a school for losers who want help building their confidence. When one of his students, Roger (Jon Heder), begins to make strides too quickly, Dr. P forces him into a one-on-one competition for the affections of Amanda (Jacinda Barrett), Roger's dream girl.

"I think that really, my biggest strength is always in the casting. I take the casting very seriously," Phillips contended. "I know that casting in a comedy is 70 percent of the battle, and if you do it right, you're more than halfway home."

When casting a scoundrel, then, Phillips needed to look no further than Thornton, who Barrett laughingly described as "a naughty boy!"

"In real life too," said Barrett, who can currently be seen alongside Zach Braff in "The Last Kiss." "He's got that irreverence and that wicked, dirty sense of humor. I think that comes across in his characters in a mischievous, devilish way."

"It's not something that you can just act," added Phillips. "I think Billy just has this thing where you think that he's up to no good."

The scoundrel is distinguished from his more roguish cousin, the jerk, in several important ways, but none is more significant than his ability to endear. There's something about just saying the word "scoundrel" that makes you grin, nod and appreciate the knave's earnest nature, his cunning attempts to trick you. He may swindle you out of house and home, but he does it with a smile. The scoundrel, it seems, isn't your typical villain -- which goes a long way toward explaining why Thornton is so good at playing one.

"I came up as a dramatic actor in a lot of independent films, but recently I have played this type of [character]," the Oscar-winning actor/writer observed. "They're just interesting. To be in these commercial comedies, playing these types of bastards is kind of fun."

Thornton saw his role in "Scoundrels" as not merely an extension of his previous work, but rather the climax of years spent portraying a string of curmudgeons.

OUR NEWEST TRAILERS
Check out the trailer premiere for Kal Penn's "Van Wilder: The Rise Of Taj," "Saw III," "History Boys" and more, on Overdrive.

"[Dr. P] is opposed to the guy in 'Bad Santa' or 'Bad News Bears' [in that] he operates with his brain a little bit more than he does with his heart, and those other guys operate more with their heart. Whatever crap they had, at the end of the day they seemed like pretty decent guys," Thornton asserted. "This guy, he is pretty manipulative. That was the tough part playing the role -- you have to make sure you never let the humanity show through. You're supposed to stay cold through the whole movie."

Phillips found the perfect foil for Thornton in relative newcomer Heder, who Barrett described as "sweet and grounded."

"[Jon] is constant good will and good nature, with a core and strength that dictates every choice he makes in a movie," the director gushed. "He's sort of an anomaly in Hollywood. He will never swear in a movie, he doesn't work on Sundays. He's just such a good person."

As the star of the cult smash "Napoleon Dynamite," Heder "gosh"-ed his way into Hollywood celebrity. According to Phillips, however, beneath that sweet exterior lies, well, something even sweeter.

"What surprised me with Jon Heder was how quickly audiences were on his side," Phillips said. "I always feel with actors, they have to spend the first eight minutes of the movie having the audience forget the baggage that [the actors] bring, and seeing them as whoever it is they are in that particular movie. With Heder, I feel like maybe because he's so new, maybe because 'Napoleon' was such a particular thing, but I feel like they're on his side from minute one."

Phillips was adamant that being able to play off the real-world personas of his famous actors helped keep the tone of the movie "real" -- which is a trait he feels all great comedies share.

"What all [successful comedies] have in common is that they are all based on reality," he said. "Basing these things on reality and being able to play off of that helps the comedy. Meaning, if you set it up in the real world, then you can be funny against that so much easier."

"Billy did his, uh, Karl from 'Sling Blade' character and Jon would do his 'Napoleon' character and they would start riffing, and a lot of the comedians were throwing down one-liners," added Barrett. "But Todd's all about approaching the material from an honest place all the time. Sometimes with some of the classically trained comedic actors, he would be pulling them back to just 'keep it real, keep it real.' When I saw the movie I was like, 'Oh yeah, I see why he's doing this,' because all of the comedy is coming out of the situation and the characters."

So in a movie about learning, what did Billy Bob teach his 28-year-old co-star?

"I learned to keep my mouth shut," Heder joked. "Things started flying and feelings were hurt, and egos were broken and hearts were mended."

And that's a lesson any scoundrel worth his salt could get behind.

Check out everything we've got on "School For Scoundrels."

Visit [article id="1488131"]Movies on MTV.com[/article] for Hollywood news, interviews, clips, red carpet photos and more.

Want trailers? Visit Movies on MTV Overdrive for the newest, scariest and funniest coming attractions anywhere.