The most believable element in “Pixels” is that alien video-game creatures could attack our planet.

The core concept is clever — space aliens misunderstand a recording of old video-games as a declaration of war, and send digital monsters based on those games to Earth as their army. But its execution in the hands of director-producer Chris Columbus and star-producer Adam Sandler is a mess.

This disappointing comedy falls apart before it begins because no one would behave the way its characters do, and their ridiculous choices drive the action.

Part of the problem is that it’s unclear who the filmmakers think their audience is. This is a big-budget spectacle about 1980s nostalgia aimed at kids who have no emotional connection to the decade. “Pixels” is also insanely sexist, culminating with the winning male characters each rewarded with a woman. Seriously, they get human women as prizes. They literally call one a trophy.

Only the film’s opening moments ring true. It’s 1982, and Sam Brenner and Will Cooper are a couple of pre-teen boys excited about the new arcade in their neighborhood. They’re so good at video games that they compete in the world championships, and Brenner almost wins. A cocky, mullet-wearing kid who nicknamed himself “The Fire Blaster” takes first.

Flash forward to present day, and Sam and Will are still best friends. Only now, Sam (Sandler) installs home-theater systems, and Will (Kevin James) is president of the United States. He launches a kids’ reading program to boost his sagging approval ratings, but he can’t pronounce the multi-syllabic words in a children’s book.

The first introduction to these guys as grown-ups is the two of them discussing which Hollywood actresses are hottest.

Will snaps into action when a U.S. territory is mysteriously attacked from the sky. Forget the elite military and special services — Will calls up Sam, the one-time video game championship runner up, hoping he might spot some arcade-inspired pattern in the airborne attack. Whaddaya know; it looks just like Galaga!

The few bright spots in “Pixels” come from the music, celebrity cameos and special effects. The soundtrack of Cheap Trick, Queen and Spandau Ballet match well with the ’80s game imagery.

And the special effects dazzle. The alien video-game creatures pixelate everything they touch. Too bad they couldn’t get their digital hands on this script.