It’s possible that the half-life of film comedy is five years. “21 Jump Street” was world-class hilarious in 2012, and Schmidt and Jenko were 95 percent as funny when they returned in this year’s “22 Jump Street.” “Dumb and Dumber,” that beloved classic, was the quality standard of downbeat dimwit humor in 1994.

Now, after a double-decade gap, Lloyd Christmas and Harry Dunne reprise their stoogery in “Dumb and Dumber To.” The result is simply stupid. This embarrassing revival plays as if the script were written in Comic Sans.

It’s not that the basic elements are missing. Jim Carrey seems to be seriously aiming for a career comeback as he reprises Lloyd, the brain-drained boob who was the nation’s dumbest dreamboat a generation back. He dusted off Lloyd’s fragmented front tooth, the childhood bowl-cut hairstyle and his love for flatulence. Jeff Daniels embodies Harry’s mental and physical awkwardness, at one point throwing his 59-year-old body down a hill in a single unbroken shot, for giggles.

There’s an early sense of nostalgic charm to see them again.

Once again, Carrey is amusingly aggressive and uncouth; Daniels is friendly and essentially harmless. But like a character here who offers the pair a friendly hug, then freaks out when they won’t let go, the reunion simply outlasts its welcome.

When it revisits the first film’s famously ribald sense of humor (with jokes involving aged co-star Kathleen Turner as a former bed-hopper, young co-star Rachel Melvin as her crackbrained daughter, and even a bawdy dog) it feels like everyone’s hormonal clock is unbalanced.

The story begins in Rhode Island, with Harry marking his 20th anniversary of visiting bearded, silent, inert Lloyd in his infirmary’s outdoor park. Ever helpful, he changes the paralyzed patient’s colostomy sack while holding the full one in his mouth. The film’s finest moment comes when Lloyd reveals his long-running lethargy was a gag. Harry, delighted, tries to get his pal out of the hospital fast by yanking out his catheter, which won’t slip free even when he asks a couple of lawn workers to help.

There’s weak continuity in what happens to the reunited village idiots. Harry announces the need of a donated kidney from his 21-year-old long lost little girl, Penny (Melvin), whose mother, Fraida (Turner), gave her to a brilliant scientist for adoption at birth. Now the girl is representing her dad’s priceless new discovery at a distant science conference like a dopier version of TED talks. The guys travel cross-country to meet her, Lloyd with kinky eagerness, under the guidance of a harebrained villain played by Rob Riggle (who was much much much better in the timely “Jump Street” series).

Along the way there are a handful of laughs, if your hands are size Small. When Harry goes through an old pile of unopened mail he smiles, “Oh, I made it into Arizona State.” When a brain scanner reveals a morally icky memory of his pubescent childhood, he denies it because “my bed sheets were orange.” Penny, who like Harry is sweet and moronic, hopes to become a volunteer in India, working at “those leprechaun colonies.”

Carrey invents the movie’s nuttiest solo just by eating a hot dog as if he were a python. But the movie drifts pointlessly through the too-long dream sequence where he fights a ninja army and seduces Penny. Directors Bobby and Peter Farrelly had one writing partner when they created the first “Dumb and Dumber” chapter. Here the credits note four Farrelly co-authors who seem to create more problems than jokes.