Dante Hicks (Brian O'Halloran) is a clerk at the Quick Stop, a local convenience store in Leonardo, New Jersey. On Dante's day off, his boss calls him in to cover a few hours for another employee who is sick. Arriving at the store, he finds that padlocks for the security shutters are jammed closed with chewing gum, so he hangs a sheet over them with a message in shoe polish: I ASSURE YOU; WE'RE OPEN! Dante is flustered at having to open the store at 6 AM when he'd just closed it the night before. He's also upset that he hasn't gotten enough sleep before having to play a street hockey game that afternoon.
Dante's day is spent in the purgatory of serving a succession of clueless and oblivious customers while bemoaning the fact that "I'm not even supposed to be here today!" His earliest customer is a man who tries to convince customers buying cigarettes that they should buy chewing gum, Chewlies brand, instead of smoking. To emphasize his point, the man shows a customer what he claims is a diseased lung that he carries in a bag. Before long, a crowd has gathered at the checkout and turns hostile at the first customer's taunts and rantings, blaming Dante for the ills of smoking because he sells cigarettes. When they start pelting him with cigarettes, Dante's girlfriend, Veronica, sprays them all with a fire extinguisher, bringing them under control. She confronts the man who recommended the chewing gum, finding out he's a representative of the Chewlies brand trying to drum up sales. She orders him out along with the mob, chiding them for having nothing better to do with their lives.
Dante and Veronica talk for a bit behind the counter about their past relationships. After a few minutes, Veronica gets up to leave and sees an old flame of hers, a guy nicknamed "Snowball". She admits to Dante that she'd performed oral sex on him and the conversation quickly escalates into an argument. She tells him that she performed fellatio on 36 other guys before she dated Dante. Dante jealously considers her past acts to be more severe than his own, which include having had sex with 11 other women before Veronica. Veronica storms out.
Interspersed with the demands of his job, Dante passes time in wide-ranging conversations with his slacker friend, Randal Graves (Jeff Anderson). Randal ostensibly works at the RST Video Store right next door, although he spends almost the entire day at the Quick Stop and is not averse to treating customers with contempt. The two converse about many things to pass time, such as whether the independent contractors working on the second Death Star when it was destroyed at the end of Return of the Jedi might have been innocent victims of the Rebels' efforts to destroy the station. Another customer offers support for Randall's theory when he tells the duo that he passed up a contracting job on a mobster's house and the contractor that took the job was killed when the house was bombed.
Veronica stops in again, bringing Dante lasagna for lunch. The two reconcile about their respective sexual pasts. She and Dante also talk about Dante's current disposition -- he's in a rut with no motivation to change -- Dante had attended college for a short period and dropped out. Veronica had transferred to a university closer to home to be closer to Dante. Further contributing to Dante's misery is an announcement shown him by Randal in the local newspaper that his famously unfaithful ex-girlfriend, Caitlin, is engaged to be married. For the previous several weeks Dante had been secretly talking to Caitlin on the phone, rekindling their relationship. Dante also talks to Randal about how Caitlin had frequently been unfaithful to Dante, once even mistaking him for another man at a party they'd both gone to separately. Randal suggests that Dante stay with Veronica since she really loves him and that Caitlin isn't worth going back to because of her infidelity.
Learning that he's stuck working the store all day because his relief skipped out to go to Vermont on vacation and the owner of the store and building is nowhere to be found, Dante convinces his friends to play hockey on the store roof. The game is short; 12 minutes into the 1st period, an irate customer climbs the ladder to the roof, demanding that Dante open the store. When the guy criticizes Dante's playing, Dante angrily invites him to play in their game. The guy wastes no time knocking Dante over in the face off and shoots their only ball off the roof and into a storm drain.
Reopening the store, Dante finds out one another of his ex-girlfriends has died and her memorial service is today. Randal talks him into closing the store again and going to the wake. The visit is disastrous, and the two are seen leaving the funeral home in a hurry and driving away, although the audience doesn't see what transpires during the memorial service. However, a conversation moments later between the two reveals that Randal knocked over the casket. Randal seems indifferent to the chaos he caused, callously saying that the dead friend didn't feel a thing.
While talking to a couple of former high-school classmates, Dante finds out that the man he's talking to, Rick Derris, was one of Caitlin's flings while she was still dating Dante. Another man enters the store and asks Dante if he's been working there all day. After a few moments, he hands Dante a court summons; Dante had allegedly sold cigarettes to an underage girl, whose mother had called the authorities. However, Dante had not been at the counter at the time, Randal had and had sold the girl the cigarettes. Dante now faces incontestable charges and a $500 fine. While he chases after the official and Derris in protest, Caitlin (Lisa Spoonhauer) suddenly appears, a surprise visit.
Dante takes her to the video store for a private conversation. After she assures Dante that the engagement announcement was premature and arranged by her overbearing and domineering mother, the two trade banter and Dante becomes torn between her and Veronica. He finally decides to take Caitlin on a date and slips home to change. He returns to discover that Caitlin has had sex with a dead man in the bathroom, having mistaken the man for Dante (the man had earlier entered the bathroom with a pornographic magazine and had suffered a fatal heart attack while masturbating). An ambulance takes Caitlin away in shock, along with the corpse.
Meanwhile, Jay and Silent Bob (Jason Mewes and Kevin Smith), a pair of stoners who've spent all day hanging out (and dealing marijuana) outside the Quick Stop, enter the store to shoplift. Dante turns down Jay's offer to party with them. Knowing Dante's predicament, Silent Bob pauses before following Jay outside and offers the following wisdom: "You know, there's a million fine-looking women in the world, dude. But they don't all bring you lasagna at work. Most of 'em just cheat on you."
Dante then realizes that he loves Veronica. When she returns to the Quick Stop, though, Randal complicates things by revealing that Dante was in love with Caitlin and is planning to date his ex again. Veronica angrily breaks up with Dante and reveals to him that Randal told her of his plans to be with Caitlin. Dante finally loses his temper and fights with Randal, making a mess of the store. Afteward, while they sit in the mess they created, Dante continues to bemoan his station in life and being stuck in a dead end job, having a girlfriend who had sex with a dead man, and that Veronica had an active sex life before she and Dante began dating. Finally losing his own temper, Randall yells back at Dante and counters everything by telling Dante that he's sick of hearing him whine about how rotten his life is and that Dante needs to think about making serious changes in his life if he wants it to improve.
The film ends with the two reconciling and cleaning up the store for the night. At Dante's request, Randal "rangles" out, popping back in briefly to toss Dante's sign at him stating, "You're closed!"