There’s a scene in the family comedy “The Pacifier” in which star Vin Diesel dives valiantly into a sewer only to emerge caked with human excrement, clutching an uncannily appropriate message: “Ha Ha.” Either Diesel acutely understands the current state of his career or someone at Disney has a very cruel sense of humor.

With high-profile failures threatening to disgrace the actor’s career beyond recognition, “The Pacifier” is Diesel’s last-ditch effort to sustain his fame; this grants this incompetent and embarrassing waste of film its own thick stench of desperation.

Navy SEAL Shane Wolfe (Diesel) is assigned to protect the children of a recently assassinated government scientist who may have hidden a computer program that’s capable of controlling foreign nuclear weapons in his house. If the premise sounds far-fetched, don’t worry. There’s actually an elaborate video-game-style minefield installed, complete with flame-shooter, falling spikes and trapdoor acid wells that must be crossed in order to gain access to the program.

The focus of the movie, unlike typical Diesel fare, is not the conspiracy, but the characters. In this case, it’s the little munchkins Wolfe must protect from the spies and terrorists seeking the program. All five kids are well cast and well used to provide humor and some vague notion that the audience should care about what happens onscreen.

Even the steely Wolfe falls for the kids as he learns to cope with his worst fear: dirty diapers. Apparently, he’s man enough to swim through sewers but is highly averse to a task most girls learn to do at age 13 for less than minimum wage. There are also those challenging baby car seats (he installs a comprehensive computerized security system, but he can’t buckle a seat belt?) and various other heartwarming parenting troubles that awkwardly collide with Wolfe’s rigidly disciplined military training. Oh, the hilarity of excessively emphasized incongruity.

Though it’s familiar, the premise is still ripe for much funnier material than this. The film’s jokes take too long to set up, and director Adam Shankman (“Bringing Down the House”) moves from one failed gag to the next with no sense of pacing or point, giving the film a lazy, haphazard feel that it can’t shake even when the story gains momentum. The whole movie becomes flat, redundant and often straight-up inept.

Diesel tends to muddle through what funny dialogue he has with a lumbering, incompetent delivery that makes any scene in which he has to react painfully strained. That said, the man can play a hardass like no one else in the business, roaring intimidating commands brilliantly. Because of this, other characters’ reactions to his authoritarian persona work to strong comedic effect; this proves to be one of the film’s much-needed saving graces.

With “The Pacifier” sucking up more than $30 million in its opening weekend, maybe that sewer-diving scene is metaphorically misleading. After all, it seems Diesel is the one finally getting the last laugh on the film’s skeptics. Ultimately, it’s the unfortunate viewing public that must wade helplessly through this kiddie pool of shit.

Rating: 1 out of 5 stars