In 2005, Corporal Joe Bauers (Luke Wilson), a US Army librarian graphed as the Army's "most average" soldier, and Rita (Maya Rudolph), a prostitute terrified of her pimp, Upgrayedd (Scarface) (pronounced: upgrade, two Ds for "a double-dose of this pimping"), are guinea pigs in a secret, year-long, military hibernation project. They are sealed in their hibernation chambers, to be awakened a year later, but the experiment is forgotten when the officer in charge, Lieutenant Colonel Collins (Michael McCafferty), is arrested for having started his own prostitution ring under the tutelage of Upgrayedd. The military base is demolished, and a Fuddruckers (eventually devolving into Buttfuckers) is built on the site.

Five hundred years in the future, their hibernation chambers are jarred open in the 'Great Garbage Avalanche of 2505', reviving both of them. Joe crashes into the house of Frito Pendejo (Dax Shepard), a typical, idiot citizen of the American future, whose dwelling is full of junk food with a prominent, giant television screen that is covered with adverts. His name, Frito Pendejo, is a haphazard combination of a product mascot (Frito Bandito) and the Spanish slang word insult.

Frito is watching Ow! My Balls!, a popular TV program that lives up to it's name with very little artistic effort. Joe is disoriented and unable to exercise the discretion necessary to allow Frito to watch his program. Consequently, Joe is thrown out the window his capsule just broke. Joe stumbles into a hospital, where slacker Dr. Lexus, MD (Justin Long), diagnoses him as simply "'tarded" and "fucked up". Dr. Lexus panics on discovering that Joe has no barcode-tattoo on his left wrist, and so cannot be scanned for automatic debit payment. Having noticed that the date of a magazine he finds on the doctor's desk (Hot Naked Chicks and World Report, 3 March 2505) has the same date indicated on his bill, Joe finally grasps that 500 years have passed since the Army put him in stasis. He is alarmed by the sights of the collapsing world (decaying buildings cabled to each other, mountains of garbage, a freeway that ends in a drop off, etc.) and flees the hospital, only to be arrested at a Carl's Jr. junk food vending booth for not paying his hospital bill and for not having a barcode tattoo.

At trial, Joe's public defense lawyer ("Attornee at Law") is Frito Pendejo, Esq., who stupidly helps convict him, citing the prosecutor's insistence that Joe is guilty and his own anger at Joe for damaging his house (in the garbage avalanche). Joe is imprisoned; a poorly-designed I.D.-tattoo machine re-names Joe as "Not Sure" (because he is not sure about his name as it appears on some form) and barcode-tattoos him as such. During a mandatory (and very simple) I.Q. test, Joe grasps just how stupid humanity has become. Easily escaping his dim jailors, Joe returns to Frito's apartment, asking him if a time machine exists to help him return to the past, to 2005. Frito claims there is one, but agrees to help only after Joe promises him billions of dollars from a savings account that Joe will open in the past upon his return. Frito is unable to understand the concept of compound interest, but takes Joe's word for it that Frito will earn 30 billion dollars minus the 20 billion dollars for expenses making 80 billion dollars.

En route to the time machine, Joe and Frito find Rita. She does not know that she's been asleep for 500 years until Joe tells her, and even then, she expects Upgrayedd will find her. Frito leads them to a city-sized Costco, where Joe is re-arrested when he accidentally allows his barcode to be scanned; instead of prison, Joe is delivered to the White House. President Dwayne Elizondo Mountain Dew Herbert Camacho (Terry Crews) has seen Joe's I.Q. test (scoring him as the most intelligent man in the world) and recruits him as Secretary of the Interior to correct the United States' food and crop shortages, dust bowl, crippled economy, mountains of garbage, and related matters. The other cabinet members are lampoons of contemporary politicians' nepotism, corporate loyalty corruption, and over-emphasis on sex appeal in political media coverage.

Joe learns that water has been replaced with Brawndo: The Thirst Mutilator (which Joe likens to Gatorade) a drink advertised as "rich in electrolytes", for virtually every purpose, including crop irrigation. The Brawndo Corporation, in an effort to boost their own sales, had, in the past, started a campaign claiming that water was only good for use in toilets. Over time, the electrolytes in Brawndo accumulated in the soil, killed the crops, and caused the food shortage. After giving up on explaining to the cabinet that electrolytes are not conducive to plant-life, Joe reintroduces the practice of watering crops. However, overnight, the Brawndo Corporation's stock becomes worthless, causing great unemployment without visibly improving the crop situation. The angry populace riot, Joe is made the scapegoat, and is sentenced to a day of "rehabilitation"; an execution disguised as a public demolition derby, billed as "Monday Night Rehabilitation". Meanwhile, Rita discovers that the soil has made crops sprout in the fields. To save Joe, with Frito in tow, she bribes a television cameraman to show the sprouting crops to the world. Before reaching the crop field, Frito and the cameraman are distracted by a sale at a Starbucks chain brothel franchise; only after they quarrel and fight does Frito remember his duty and film the crop sprouts. President Camacho sees the thriving new plants on the stadium's big-screen televisions, and grants Joe a pardon just as he is about to be incinerated with a flamethrower.

At the celebration, Joe decides to stay and help repair American civilization; President Camacho names him Vice President of America. He also learns that the "Time Masheen" is just an amusement park ride, with a historical theme, wherein Charlie Chaplin was leader of the Nazi party who used dinosaurs to wage war on the world, and the U.N. (pronounced "The Un") "Un-Nazied the world forever". Joe serves a short term as Vice President, then is elected as Camacho's successor. Joe and Rita marry and have the world's three smartest children, while Frito Pendejo takes eight wives and fathers thirty-two of the world's stupidest children, echoing the introduction to the film.

After the credits, a third hibernation capsule is shown opening, releasing a snappily dressed Upgrayedd into the world, who struts down the street, as a pimp is wont to do.