Not even Robert Downey Jr's typical wit can revive lousy material. The charismatic actor plays Peter Highman, an architect with something of an anger management problem. He has a tendency to snap at people over trivial things, which gets him into trouble. His wife Sarah(Michelle Monaghan) is days away from delivering their first baby, and he's got to hop a flight in order to be there in time. Should be easy, right? Atlanta to Los Angeles is a long flight but not impossible. Well, it is if you're on the No Fly List. Why's he on the list reserved for terrorists and folks with too many Q's in their name? Because of a literal run-in with Ethan Tremblay(Galifianakis), a strangely effeminate, Grizzly Adams bearded wannabe actor, really just an idiotic tornado of destruction. He carries his little dog in a purse like the fattest, ugliest Paris Hilton you'll ever see. His very presence pisses Peter off, and an airplane Marshall wasn't havin' it. Both are kicked off the flight, and an easy journey home just got a lot tougher.
With no money, Peter is forced to tag along with Ethan for the journey back home. It's a disaster from the instant foot meets pedal. The two travelers predictably mix like oil and water. Peter constantly warns Ethan that his temper might get the better of him(of course it will), while Ethan doesn't seem to realize how much of a dunce he really is. Any number of contrived obstacles are thrown in their path. Danny McBride shows up as an angry, violent, handicapped veteran. Jamie Foxx inexplicably shows up as Peter's best friend and Sarah's ex-boyfriend. A lousy, half hearted subplot crops up that throws some doubt into the parentage of Peter's kid. They should've just left that part out.
And then there's Ethan and his desire to spread his recently deceased father's ashes somewhere memorable. This particular storyline pops up when convenient, but has no genuine emotion behind it at all. Ethan carries his father's ashes around in a giant coffee can. Can you maybe guess what happens when everybody needs a drink later on? Yeah. It's all very predictable even by road trip standards. For instance I bet you already know there's a male bonding scene where both guys get high on too many illegal drugs. I'll just bet you saw it coming. Everything is telegraphed from two miles away.
Being predictable doesnt' necessarily make for a bad movie. Road trip movies are almost all the same. They all take liberally from the Planes, Trains and Automobiles
formula. A pair of wacky mismatched dudes face ridiculous obstacles to get from point A to point B. That much is fine, but what Due Date seems to forget that part of what made that movie a classic is that both Steve Martin and John Candy's characters felt like real people. I've met people like Del Griffith before. People who just want to be helpful and friendly but are irritating and a little bit aimless. The characters in Due Date don't feel real at all, so it's hard to sympathize during the few attempts at poignancy. There are a few jokes that work like gangbusters, mostly revolving around Ethan's obsession with Two and a Half Men, but finding one you haven't already seen in the numerous trailers is tough. 
