Late one Saturday night at Bar Lubitsch, a West Hollywood cocktail bar known for its kitschy, Soviet-era décor and frosty vodka drinks, Scott Korinke and Nolan Marks wriggled themselves from the sweat-drenched dance floor and made their way to the bar counter.

Mr. Korinke, 26, ordered a martini for himself and a vodka Red Bull for his friend Mr. Marks, 25. As he fished a Visa credit card out of his green leather wallet, the bartender yelled out a question over the music: “Do you want to start a tab?” Mr. Korinke shook his head no and swiftly closed out.

The pair might order more drinks later on, but the prospect of opening a tab was verboten. “Why leave a credit card with the bar? I don’t know if I’m going to be here that long, so I don’t want to leave a tab open,” Mr. Korinke said, joking that he had “commitment issues.”

His ethos reflects a growing phenomenon among Gen Z bargoers: an aversion to opening bar tabs. Much to the dismay of bartenders, many 20-somethings prefer to close out and pay after every drink, no matter how many beverages they end up ordering.

The reasons for this are myriad. For a generation that consumes less alcohol than older drinkers, opening tabs can seem exorbitant. They have become accustomed to one-and-done transactions — usually with a simple tap of their phones — and consider purchasing drinks at a bar to be no different from, say, buying a coffee at a cafe. They can feel anxious about losing track of their spending by leaving their credit cards behind the bar.