And they're on a tight schedule. Peter needs to get to Los Angeles in four days for the birth of his son by scheduled C-section. With wallet stowed in his bag on the plane, Peter depends on the kindness of the very strange stranger, a fey narcoleptic with glaucoma, a stash of medical marijuana, and less concept of cause and effect than a newborn.
In this film, written by a tag team of four scribes, the basic premise is that if you want to make God - or anyone else - laugh, make a plan. Plans, like Peter's carefully thought-out itinerary, never take into account those necessary detours to rest stops, drug dealers, and border crossings.
Playing to type as Ethan, Galifianakis, the ginger-bearded bear of a boy who shot to fame as the odd-duck brother of the bride in The Hangover, is funny not because he is boorish but because he is immune to embarrassment. Playing against type as Peter, arbiter of appropriateness, Downey is funny because in spite of his character's carefully managed rage, he loses control at the most inappropriate times.
I winced more than laughed at this movie, which has almost as many broken bones as punch lines. But there is something comically symmetrical about Downey as an expectant dad rehearsing fatherhood with the overgrown boy and Galifianakis as the fatherless son who adopts Downey as his surrogate dad.
Contact movie critic Carrie Rickey at 215-854-5402 or firstname.lastname@example.org. Read her blog, "Flickgrrl," at http://www.philly.com/philly/blogs/flickgrrl/