YOU CAN look at "Due Date" as a foulmouthed "Planes, Trains and Automobiles," or as "The Hangover 1.5," something to tide you over until 2.0 arrives.
"Due Date" offers the director (Todd Phillips), a slew of bit players from "The Hangover" and a healthier (if that's the right word) dose of Zach Galifianakis, the breakout star of "The Hangover," who is effecting a swift and somewhat hostile takeover of movie comedy.
In a pop-culture instant, the hairy, stammering misfit has gone from obscure stand-up to box-office dynamite. Now he's leapfrogged the ensemble and become top-of-the-marquee big, maybe bigger than some of his co-stars would like.
Even float-like-a-butterfly Robert Downey Jr., who had no trouble dancing around a Russian-accented Mickey Rourke in "Iron Man 2," seems slightly flustered in "Due Date" by Galifianakis' black-hole ability to suck all energy into his oddball orbit.
All good actors have the ability to be unaware of the camera. Galifianakis, though, often seems to be unaware of his co-stars, of his surroundings, of the fact that he's in a movie at all.
His face registers that he lives in a private world of his own imagining, which is all to the good, because we sense we don't want to know what's going on in there - there's the sense of actual derangement, acknowledged recently in "It's Kind of a Funny Story."
In "Due Date" he's more safely funny as Ethan, a weirdo loner who ruins what is meant to be a short cross-country flight for architect Peter Highman (Downey), rushing home to attend the C-section of his wife (Michelle Monaghan).
Ethan instigates a series of mishaps, and the two men end up sharing a rental car on an odyssey that's a nightmare for Peter. Ethan, he learns, is a dope fiend, a chronic masturbator, a deadbeat and worse - an aspiring actor.
Peter does little to hide his contempt, and as his anger grows, it explodes in a series of "oh no he didn't" moments - Ethan insults a Gulf War veteran, for instance, and punches a child. The latter gets big laughs, but they're cheap, and this is really an area that self-styled "transgressive" filmmakers should avoid.
You can feel "Due Date" aiming, a little desperately, for "Hangover"-style shock laughs. More work should have gone into helping Downey and Galifianakis make sense of their characters, so that their ultimate buddy hug makes more sense.
Fans of "The Hangover" can mostly have fun spotting supporting players from the 2009 movie. (Probably a great cast party.) The reunion of Downey and Monaghan, so good together in "Kiss Kiss Bang Bang," is less momentous, since poor Michelle has nothing to do here, and hasn't had much to do since her smashing breakout back then.