Nerdy college student Alistair McDowell moves in with Larnell [John Patrick Jordan], a law school dropout, and his two roommates—the laid-back Bachman and former baseball player Brett. When Larnell spots an online ad for a gigantic bong that the previous owner claims is possessed, he orders it. They receive the mysterious object and, despite Alistair's reluctance, they light it up. The group starts smoking, though Alistair remains clean. During this early haze, Alistair meets Brett's girlfriend Luann and her friend Janet, and a quiet crush begins to form between him and Janet.
That very night, Bachman’s soul is dragged into The Bong World, a hellish, seedy strip club that exists inside the Evil Bong. There he encounters Ooga Booga and Ivan Burroughs, who warn him to beware the cursed device. A stripper with skulls on her bra bites his neck as Ooga Booga looks on, and Bachman dies. The next morning, the roommates discover Bachman dead on the couch. Alistair suggests it was the weed, but Larnell points out that they all smoked and notes that the bong has changed—the face of the device now seems to watch them. They hide the body, hoping to cover their tracks, but their troubles multiply when Cyril, Larnell’s paralyzed, wealthy grandfather, stops by to announce he has remarried.
Soon the bong itself begins to speak to Larnell, a voice that only he can hear, and it tempts him to take another hit. He succumbs, and is pulled into the Bong World, where he stumbles upon Bachman—who appears to be perfectly fine—alongside the Gingerdead Man and Cyril. A stripper in this world gives him a hypnotic lap dance, and Larnell is killed in the same brutal way Bachman met his end. Back in the real world, Luann and Janet come over, and the trio—minus Alistair—smokes again. Brett and Luann fall unconscious, only to wake inside the Bong World, where they’re greeted by Jack Attack. Luann is seized by a bouncer, while Brett encounters his ex-girlfriend Carla Brewster, a Bong World stripper, who uses a predatorily cupped bra to bite off his genitals, killing him.
Janet also falls prey to the Bong, and Jimbo Leary enters the scene to claim ownership of the cursed device. He proclaims that the bong, Eebee, Michelle Mais is his and that it carries a voodoo-like curse: once someone takes enough hits, they are dragged into the Bong World where the bong closes in on them. To rescue Janet, Alistair bravely enters the Bong World. Jimbo makes several valiant but futile attempts to destroy the bong—hammer, chainsaw, and even a bomb—but Eebee releases a smoky cloud that knocks him unconscious.
Inside the Bong World, Eebee tries to seduce the remaining victims, forcing the captured strippers to lure Alistair, though he fights off their advances. He soon encounters Jack Deth and uncovers Janet’s location. Eebee reveals her grand plan: she intends to turn the air into a perpetual pot-smoke and transform the oceans into bong water, effectively making everyone a massive stoner. They ingest “vitamins” from Jimbo to regain sobriety and escape their bonds. Jimbo, who is dragged into the Bong World himself, urges them to flee while he tries to contain Eebee. He reveals a time bomb strapped to his chest, activates it, and blows up Eebee.
Back in the real world, the gang’s souls are returned, and everyone comes back to life. The bong is shattered, and Jimbo is believed dead as well, though the ending hints at his continued strange presence as the new king of the Bong World.
