Wait a second. You’ve been standing in line for 20 minutes, famished and desperate to order one of the viral bagels that keep selling out—or for six hours outside a concert venue, determined to claim a spot at the barricade to see your favorite band.

And then someone strolls up and slips in line ahead of you. Apparently, the rest of you have been standing around for the ambiance.

How much of a sin are line-cutters committing? “You are ripping the fabric of society apart,” says Nick Leighton, an etiquette expert and co-host of the podcast Were You Raised by Wolves? Queue-jumpers have to live with that, he adds. “But worse, we have to live with you.”

Here’s exactly how to handle this maddening situation—including when and how best to speak up.

When to speak up about someone cutting in line

If a stranger jumping ahead of you feels strangely personal, Richard C. Larson, a professor emeritus of data, systems, and society at MIT who has studied queuing, understands why. “We only have a finite number of minutes of life on Earth,” he says. The cutter’s implied message: “A minute of my life is worth more than a minute of yours.”

Before you decide whether to confront the offender, think about what speaking up would accomplish. Are you trying to reclaim your turn or get revenge? Sometimes, the impulse is “to sort of let them know you think they’re a jerk,” says Ryan Martin, a professor of psychology and dean of the College of Arts, Humanities and Social Sciences at the University of Wisconsin–Green Bay, known online as the Anger Professor because he studies strong emotions.

Martin would speak up to help someone recognize “that what they did wasn’t OK and that I wanted them to go to the back of the line,” he says. But he’d also consider: “What is going to allow me to have the kind of night I want to have?” If you spend the concert replaying a confrontation instead of singing your happy heart out, you’ve lost more than your place in line.

Leighton’s gut check for situations like these is to ask yourself: Is this the hill you want to die on? “That’s always a good etiquette question,” he says.

Consider your safety, too. If the person seems hostile or you feel uneasy approaching them, you can ask staff for help or let the cut go. “Health and safety always trumps etiquette,” Leighton says.

What to say—if you do decide to say something

Marie Helweg-Larsen, a professor of psychology at Dickinson College who studies social norms, has explored what makes line-cutting so rage-inducing. For a 2008 study, she and a colleague surveyed U2 fans waiting for prime concert-floor spots, asking how they would react to hypothetical line-cutting scenarios.

Interestingly, fans reacted just as negatively to someone cutting behind them as ahead of them—even though their own place wasn’t affected. “You have to have people follow the rules,” she says, “or your investment into the line falls apart.” Helweg-Larsen’s co-author also heard fans invoke a higher authority when someone misbehaved: “Bono wouldn’t like that!” 

You don’t need a rock star’s moral authority—or a grand speech—to point out where the line starts. Helweg-Larsen’s suggested opener: “Excuse me, but the line starts down there.” Aim for an “‘I’m just trying to be helpful’ kind of vibe,” she says.

That approach gives the person a chance to correct their mistake without having to defend their character. And you don’t have to believe it was an innocent oversight to deliver the message graciously. “Even if they’re doing it on purpose, you still need to use that tone,” Leighton says.

He’s been on the receiving end of a polite correction himself: At a deli, he once joined what he thought was the back of the line, only to discover he’d guessed wrong. He was happy for someone to point him in the right direction.

If you decide to speak up, do it promptly. “Your window of opportunity is short,” Leighton says. “As soon as it happens, that’s when you need to say something.” Waiting until you’ve spent five minutes glaring at the back of someone’s head won’t make the conversation any easier.

For a line that represents a serious investment of time, Martin suggests spelling that out: “Hey, I’m not sure you noticed, but there’s actually a really long line here, and people have been waiting all day.” You’ve identified the problem and given them an opening to say “Oops.”

Of course, some situations are murkier than a stranger breezing past the entire queue. Someone returning from a bathroom break is different from four friends arriving hours later to join the person who saved their places. Leighton is sympathetic to a water or restroom run. Holding spots all day for a last-minute entourage? “I don’t love that,” he says.

What to do if a line-cutter won’t move

Sometimes, your kind reminder won’t be met with the same level of helpfulness: They saw the line. They’re staying put. Now what?

If you feel comfortable continuing, Martin suggests a firmer follow-up: “I really think you should go back to the back of the line.” You’re making a direct request without adding an insult.

Larson advises skipping any confrontational nicknames or demands—like “What do you think you’re doing, bud?” You’re pointing someone toward the back of the line, not challenging them to a duel.

If the person still refuses to move, resist the urge to keep arguing. “We can’t control everybody,” Martin says. Continuing to push someone who’s already refused could lead to “a more significant confrontation.”

At a concert venue, amusement park, or other staffed location, you can ask an employee or security person to step in. “You can always appeal to a higher authority,” Leighton says. Whether they’ll enforce the rules is another question, but it’s an option worth trying when the cutting is particularly egregious.

If you decide to drop it, drop the parting shot, too. A sarcastic “Must be nice!” might feel irresistible, but Leighton advises against adding more rudeness to the encounter. “It will not achieve anything,” he says.

As Larson puts it, “A fight can ruin your whole day—or life.”