Two obnoxious and unlikeable people are stuck together for an excruciating cross-country road trip that is hard on them and harder on the audience.  It is such a thoroughly unpleasant journey that it forced me to reconsider my previously firm conviction that I would happily watch Robert Downey, Jr. in anything.  I stand corrected.

Downey plays Peter, an architect in Atlanta on business who has to get home to Los Angeles for the birth of his first child.  At the airport he has a meet-uncute encounter with man-boy Ethan (Zach Galifianakis, rapidly depleting the goodwill from his fine performance in “It’s Kind of a Funny Story”).  A few sharp words and an inadvertent exchange of some personal effects and no one but the characters is surprised when they end up on the same flight and are immediately booted off and put on the no-fly list. 

Various slapstick catastrophes occur filmed with a surprising lack of energy and interest by director Todd Philips (“The Hangover,” “Old School”), who seems as uncomfortable and distracted. Perhaps that is why he failed to consult with Downey on exactly what his character is supposed to be doing in this film. I don’t mean getting from Atlanta to LA or even having alternate meltdowns and blow-ups. I mean — is he the everyman we are supposed to identify with, a counter-balancing order to Ethan’s chaos?  Is he the guy who seems together on the surface but turns out to be even more of a needy mess than the big delusional baby with the beard and the mincing walk? Is there any way not to wince, given Downey’s real-life history, when his character has to get all trippy?  The ghost of “Planes, Trains, and Automobiles” haunts this joyless mess.