Robert Downey Jr and Zach Galifianakis play mismatched travelling companions, a very odd couple stuck together on a hellacious (for them) but hilarious (for us) cross-country journey.

Frazzled businessman Downey Jr is anxious to get back home to his wife in Los Angeles in time for the birth of their first child.

Attempting to catch a flight from Atlanta, however, he inadvertently gets mixed up with irritating wannabe actor Galifianakis and ends up thrown off the plane and sharing a chaotic, disaster-strewn car ride with him across country.

They are not people you’d care to have sitting next to you on the shortest of bus trips, let alone a 2,000-mile car journey, but, even though writer-director Todd Phillips, maker The Hangover, pushes our sympathy for them to the limits, the inspired comic playing of Downey Jr and Galifianakis ensures that this road movie comedy is well worth the ride.