American movies overflow with arrested-development cases. (There’s something very American about that.) Yet it’s not every day that you see an engaging indie comedy about “adulting” — that is, characters of a certain age who are still sealed inside the youth bubble, to the point that they regard conventional grown-up activities like holding down a job or taking care of another person as beyond-their-pay-grade endeavors.

The smart and fluky “Sacramento” is that kind of movie. It’s been called a road comedy, and technically it is, if you count as a road comedy a film in which the two main characters are old friends who may no longer even like each other, who climb into a vintage gold Chrysler Imperial — the car they shared in their youth — and drive from L.A. to Sacramento, a trip that takes all of six hours (and occupies about 25 minutes of the movie).

Why are they going there?...