The odd couple road trip is a venerable, oft-repeated movie formula. Come up with a pair of guys who can't get along, find a crazy reason -- the wackier the better -- for them to be stuck in a car together for thousands of miles, and your work is half done. This is precisely what writer-director Todd Phillips (with three co-writers) does with Due Date. The movie rips off (or pays homage to) Planes, Trains, and Automobiles (1987), and a host of other road movies in telling the tale of an anxious father-to-be and a shlubby wannabe actor on the road from Atlanta to Los Angeles. (Phillips is apparently a fan of the road trip formula, having already made a road trip movie, cleverly called Road Trip. He also directed last year's megahit The Hangover, and specializes in movies about men behaving badly, of which Due Date is also an example.)
Peter Highman (Robert Downey, Jr.) is a tightly-wound architect. His wife (Michelle Monaghan) is about to have a baby, by scheduled C-section (a fact the movie delivers, but never explains). Soon-to-be-pater Peter runs into man-baby Ethan Tremblay (Zach Galifianakis) at the airport in Atlanta. Actually, Ethan runs into Peter, literally, and takes the door off his limo. This is but the first in a series of unfortunate events that eventuates in both Peter and Ethan being thrown off their flight, and placed on the no-fly list. Peter loses his wallet in the process, and is thus forced to ride with Ethan in a rental car, all the way to Los Angeles. Ethan is heading to Hollywood to meet with an agent. He's an aspiring actor. His aspiration is, primarily, to appear on the sitcom Two and a Half Men. Peter just wants to get home in time for the birth of his first child.
Ethan has a french bulldog named Sonny, and a coffee can containing his father's ashes. He also has "glaucoma," which he "treats" with copious amounts of "medical" marijuana, which he buys from dealers he finds on the internet. He's not a very good driver (which is probably true even when he isn't stoned), he's not very smart, and he's a terrible traveling companion. Among other things, both he and his dog masturbate a lot. In the car. Peter suffers a great deal of physical pain and injury, mental anguish, and legal trouble on the hellish journey, and lashes out at Ethan -- which Ethan completely deserves. All of this is a recipe for male bonding, no?
It has to be, because bonding is the point of the movie road trip. Peter (who isn't so good with kids, it turns out) is stuck with a big man-baby who is every bit as uninformed, self-absorbed, destructive, and oblivious to danger and social mores as the average two year old. This is the sort of character Galifianakis specializes in, and it isn't much of a departure from his character in The Hangover, although that guy both was a baby (figuratively) and carried around an actual baby. Ethan just carries his little self-pleasuring dog around. He is appalling, an oversized character in a clumsy, oversized body -- he's got quirks and personality to burn. At his core, he's innocent -- the damage he does is unwitting and unintentional. Downey's Peter, on the other hand, is an underwritten character whose personality traits are fussiness about baby names and a tendency to get apoplectic when provoked. He is provoked frequently, of course. Neither of these guys becomes any less, or more, in the course of their odyssey -- they arrive at journey's end much as they were at journey's beginning, although Peter is much the worse for the wear. Much of the appeal of the movie, of course, is that Downey and Galifianakis are opposites in so many ways that they make the incendiary chemistry between Peter and Ethan credible, even if the circumstances of the plot are forced. Both actors are good enough that they even manage to sell (mostly) the warm and fuzzy ending to this buddy comedy.
The plotting of Due Date is hectic and extravagant, the comedy is uneven but fitfully funny. When it's funny, it's quite funny, though in a nasty, calculatedly outrageous way.