The moment “Zonad” clicked for me was about halfway through, when Cinematical editor Erik Davis leaned over and whispered, “This is like a ‘Simpsons’ episode.” Yes! Exactly! I mean, you shouldn’t talk during the movie, but yes! The cheerfully implausible story line, the dimwitted but recognizable townsfolk, the cartoonish disregard for reality — if everyone were painted yellow and missing a finger on each hand, you’d swear Fox had commissioned an Irish translation of a season 10 episode.

“Zonad” is actually the work of brothers John and Kieran Carney. John wrote and directed the sweet indie hit “Once” a few years ago, but “Zonad,” based on an unreleased short film the Carneys made in 2003, couldn’t be more different from that. The Tribeca Film Festival program calls it a “zany romp,” which makes it sound awful — I think the same description appears each week in TV Guide next to “According to Jim” — but no, it really is a zany romp, in the best possible way.

A quaint Irish town called Ballymoran is the setting, where one night the Cassidy family comes home to find a visitor from space unconscious in their living room. They know he’s a visitor from space because he’s wearing a red vinyl suit and a helmet, and because everyone just came from a stargazing event that got them thinking about the possibility of life on other planets. The people of Springfie– er, Ballymoran are highly suggestible.

Zonad (Simon Delaney), as he calls himself, is not an alien. His name is Liam, and he escaped from a nearby alcoholism rehab center and got plastered on the Cassidys’ booze. But the alien thing is a useful fiction, so Liam runs with it, adopting an “alien” voice that’s somewhere between Capt. Kirk and Data. Now he has a place to stay and plenty of liquor to drink, and gets to be around the lovely Cassidy daughter, Jenny (Janice Byrne). The other Cassidys — Dad (Geoff Minogue), Mom (Donna Dent), and little Jimmy (Kevin Maher) — are hospitable and gracious hosts.

Soon Zonad is a town celebrity. What village wouldn’t be proud to have an extra-terrestrial in its midst? (The exception is Jenny’s prudish boyfriend, played by Rory Keenan, who doesn’t trust the guy.) Complication arrives in the form of Francis (David Pearse), who escaped from the rehab center with Liam and was briefly delayed. Now he shows up in Ballymoran, too, sees the scam Liam is pulling, and declares himself to be a fellow alien named Bonad. First one alien, now a second one! A BETTER one! It is the most exciting week in Ballymoran’s history.

The town and its people seem locked in a 1950s mentality: trusting, naive, old-fashioned. (I’m not familiar with the small towns of modern Ireland, so forgive me if they’re really like this.) This is necessary for the film’s story to work, but it also brings to mind the invaders-from-space B-movies of the ’50s that “Zonad” affectionately emulates.

I’m pleased to report that the film has no interest in teaching its characters valuable lessons. Any learning or growing that occurs is purely accidental, and comes after the ribald jokes and scattershot, anything-for-a-laugh plot line. (The showdown between Zonad and Bonad, held in the town square, somehow involves a “Raging Bull” reference.) Just 78 minutes in length, “Zonad” is short, slight, and not very substantive. But it’s infectiously upbeat and good-natured, which helps even the goofiest, most absurd jokes go down smoothly.

B (1 hr., 18 min.; Not Rated, probably R for some harsh profanity, some strong sexuality.)