The movie opens with spoofing "Armageddon" and "10,000 B.C."
In the year 10,001 B.C., a caveman Will (Matt Lanter) runs away from a mammoth before getting in a fight with Wolf (Ike Barinholtz). He then encounters a saber-toothed, gasoline-drinking Amy Winehouse (Nicole Parker), who informs him that the world will end on August 29, 2008 (which was the film's opening day and Michael Jackson's 50th birthday), revealing their fate laying in a crystal skull "Indiana Jones". The film flash-forwards to the present, where Will apparently dreamed all of this. He then finds out that his girlfriend, Amy (Vanessa Minnillo), is having an affair with Flavor Flav (Abe Spigner) and the two break up with Will not admitting his true feelings for her.
Later that day, Will has a "Sweet Sixteen" party at his house, despite the fact that he's 25. Among the guests are Juney (Crista Flanagan) spoof of "Juno" and Will's best friend Calvin (Gary "G-Thang" Johnson), who attempts to curve a bullet around the room "Wanted" to stop Seth and McLover "Superbad" (Noah Harpster and Austin Scott) from stealing the alcohol, accidentally killing "Dr. Phil" (John Di Domenico), Anton Chigurh (Barinholtz), and the Beautiful Assassin (Carmen Electra) in the process. By then, Amy arrives with her new boyfriend, an underwear model (Nick Steele), before the "High School Musical" number is performed with cameos by an off-key Jessica Simpson (Parker) and Justin Timberlake (Jonas Neal).
However, the party comes to a halt when the lights go out as the room shakes and a bulletin on the radio claims that it is the end of the world. Will, Juney, Calvin and his girlfriend Lisa (Kim Kardashian) go outside during a meteor shower and find that "Hannah Montana" (Flanagan) has been crushed by a meteor and, even when caught between life and death, is still promoting her merchandise until her wig falls off, revealing her as Miley Cyrus before she finally dies. While this occurred, a kid (Ty Wesley) wakes up "Hancock" (Walter Harris) and mouths at him to go save the world, only to be knocked away as Hancock tries to flee the city but hits his head on a streetlight and knocks himself out. Soon after, the city starts to freeze over, and the group retreats to a garage for shelter. They meet the "Sex and the City" girls, who claim to have first grabs and Juney beats a drag queen version of Carrie Bradshaw (Jason Boegh) for the garage "Don't Mess With The Zohan". After discussing global warming, Calvin says that he is cold and suggests they take their clothes off. Only the girls take their clothes off, and the guys stare in awe until Juney's water broke.
Later, Will has a dream where he is a "Jumper" and accidentally impales himself on Prince Caspian's (Barinholtz) sword (Caspian identifies him as "the guy who ruined Star Wars"; also a reference to Matt Lanter's voice role as Anakin Skywalker in the 2008 CGI Clone Wars television series). After Will's dream ended and he was chided for not even trying to commit to his relationship, the gang leaves the garage and Will gets a call from Amy, admitting his feelings for her before he decides to get to her as Lisa gets killed by a meteor. While the others comfort a distraught Calvin, the "Enchanted" Princess climbs out of a manhole and gets hit by a taxi, with Calvin catching her as they immediately fall in love with each other. Juney guesses she's a princess thrown out of her kingdom by an evil witch, the Princess explains that she's a "demented homeless chick who lives in the sewers" due to consuming "lots and lots and lots of mind-altering, enchanting drugs!" After getting into a dance off with the Princess's Princely pimp dancing to Sizzle C's 'I Like Them Girls', the heroes flee when a tornado appears with "Iron Man" (Gerrard Fachinni), "Hellboy" (Barinholtz), and the "Incredible Hulk" (Roland Kickinger) attempting to fight the natural disaster and being knocked down by its projectile cows. When they find shelter, Calvin gets a call on his shoe phone from Lisa's mother, who is informed about Lisa's death and how Calvin has found someone hotter than Lisa. Afterward, they encounter a group of cute singing chipmunks "Alvin and the Chipmunks" who suddenly turn rabid, attacking the gang and eating Juney's flesh until she presumably dies. The chipmunks go after the others until Calvin and Will trap them in a trash can, suffocating them as they attempt to break free.
On their way to the museum to save Amy, who called to tell Will she's trapped under a statue, they run into "The Dark Night" (Barinholtz), who informs them that they must go to the evacuation buses by 9 p.m., and also mentions that there will be no chance of survival if they go to save Amy. Learning that it's closer to nine than he thought, Batman throws a rope, which accidentally lands on a car that drags him away. With time against them, the Princess kills "Speed Racer" (Jared Eddo) so they can hijack his car with Michael Jackson (Christopher Johnson) in the trunk along with Chim-Chim and Spritle, and drive to the museum. When they get there, they save Amy who reveals the Crystal Skull from Will's dream to be the only thing that can stop the end of the world. As Will and Amy make their way to the altar, Calvin and the Princess find that the museum doors are closed and all the artifacts have come alive "Night at the Museum", including "Kung Fu Panda" (Yoshio Iizuka), who fights Calvin. When Calvin makes out with the Princess after beating him, he sees that she is actually a transvestite by removing "his" wig while the Panda takes out a katana and kills them.
Meanwhile, Will and Amy run into "Beowulf" (Barinholtz), who fights Will in the nude. After Beowulf is defeated, Will and Amy meet Will's father (Tony Cox) and Will returns the Crystal Skull to its altar, averting further destruction. The film ends with a wedding ceremony for Will and Amy being performed by "The Love Guru" Shitka (John Di Domenico). Then all the characters come sing a song about dating each other which sets of a chain "Disaster Movie F**k Song" ending with the chipmunks being crushed by yet another cow.