Dante Hicks, a young man who works as a retail clerk at Quick Stop Groceries in Leonardo, New Jersey, is called into work on his day off to cover another employee’s morning shift. Arriving at the store, he finds that the locks to the security shutters are jammed closed with chewing gum, so he hangs a sheet over them with a message written in shoe polish: “I ASSURE YOU; WE’RE OPEN!”. Soon after opening, Dante’s best friend, wisecracking slacker Randal Graves, arrives for his own workday at the video rental store next door.
The two prepare for another ordinary day immersed in their tedious customer service jobs. Dante repeatedly laments that he is “not even supposed to be here today,” while Randal neglects his job at the video store to keep Dante company at the Quick Stop. They pass the time engaging in philosophical discussions on a wide variety of topics, including movies, sex, relationships, and difficult customers. Some of the customers they encounter during the day are angry and demanding; others, clueless and impolite; still others prove unexpectedly wise. After several hours, Dante discovers that his boss has left on a trip to Vermont, leaving him to run the store alone for the rest of the day. Dante and Randal find a number of reasons to leave the store and slack off, from a rooftop hockey game with Dante’s friends to an ill-fated wake for one of Dante’s ex-lovers.
Dante is torn between two women: his current girlfriend Veronica Loughran and his ex-girlfriend Caitlin Bree, with whom he still secretly communicates. Dante is distressed when he learns Veronica has given oral sex to 36 other men before him, and engaged in snowballing with at least one. Despite Veronica’s doting on him, Dante chooses to rekindle his relationship with Caitlin. However, Caitlin is traumatized by an incident in the Quick Stop bathroom; in the dark, she has sex with a person she thought was Dante, but who was actually a customer who had died of a heart attack while masturbating to a pornographic magazine Dante provided him. Caitlin leaves catatonic in an ambulance.
Jay and Silent Bob, a pair of drug dealers who have spent the day loitering outside the store, invite Dante to party with them after hours, but Dante declines, considering the various seedy characters the two have been attracting all day. Aware of Dante’s problems, Silent Bob tersely convinces him that he really loves Veronica, but Randal has already confessed the previous events to her, prompting Veronica to dramatically dump Dante. Dante fights with Randal, trashing the Quick Stop.
Dante and Randal have a crucial moment of clarity after their fight. Randal hears Dante repeat his refrain that he’s “not even supposed to be here today” and points out that Dante could have left at any time and prevented the day’s events; furthermore, he says they are not as “advanced” as they think they are, or else they would not be stuck in such lowly jobs.
After the two make amends, Dante plans to visit Caitlin in the hospital and try to reconcile with Veronica. Randal leaves, but not before tossing Dante’s shoe-polish sign in his face and declaring, “You’re closed!”