Like Steve Martin and John Candy before them, Robert Downey Jr. and Zach Galifianakis are two guys who should never get stuck traveling together.
In "Due Date," opening Friday, Downey and Galifianakis take a mishap-filled road trip reminiscent of Martin and Candy's travel debacle in John Hughes' 1987 comedy "Planes, Trains and Automobiles."
The characters and details are different, but the two movies share a few key traits: Two strangers, an uptight establishment guy (Downey) and a ball of chaos (Galifianakis), are forced to hit the highway in each other's company.
"The nice thing about being arbitrarily partnered with a stranger that's a nightmare is that you get a great story," Downey said. "The trip only has to last so long, and the story lasts a lifetime. The difference in 'Due Date' is, that stranger is putting you in mortal danger."
Downey stars as Peter Highman, a man heading home from Atlanta to Los Angeles to be with his wife for the birth of their first child.
Grounded by an incident before his plane takes off, Peter winds up on a cross-country car trip with aspiring actor Ethan Tremblay (Galifianakis), a big-hearted innocent with no social restraint and a habit for causing traffic mayhem.
"Ethan is essentially playing the starter kit for Peter's well-in-need-of-anger-management parenting course," Downey said. "Then again, I think one would be able to be Octopop and still not survive Ethan."
Galifianakis said "Planes, Trains and Automobiles" is his favorite road trip movie and that one of the film's funniest scenes comes as Candy's character takes off his shoes and socks then fans his bare feet on an airplane, oblivious to the other passengers.
"Space invaders, or whatever you want to call them, when you travel are the funniest. People that don't realize there are other people around them," Galifianakis said. "For some reason, that part of their brain is missing."
"Due Date" is director Todd Phillips' follow-up to last year's comedy smash "The Hangover," another tale of mismatched traveling companions (Galifianakis among them) whose bachelor bash in Vegas turns to disaster.
Phillips' credits also include 2000's comedy "Road Trip," so mixing travel and laughs is something of a specialty.
"It really presents an opportunity to put your characters through the paces. They're kind of out there without a safety net, so to speak," Phillips said. "When you set a movie, let's just say, in your hometown, you have the support of your family and your friends, your life.
"There's something about when you go out on the road. You're just operating outside your comfort zone. Particularly if you're with a stranger, somebody you don't know, and somebody who may not be the best traveling companion."
While his "Due Date" character is a highway menace, Galifianakis said he would rather travel with Ethan than with Downey's combustible Peter.
"I have more tolerance for stupidity than I do rudeness," Galifianakis said. "Also, stupidity makes me feel smarter."