Airports are the worst, right? Long lines for security screenings are bad enough without fellow passengers mucking up the works.

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Consider what happened at Newark International Airport back in November 2001. A man made it through security but realized he forgot his camera bag. He jogged back to an unsecured area of the airport to retrieve it. Then, afraid he’d miss he flight (and a football game at his destination), he did an end run of his own, going down an “up” escalator and entering a secure area without going back through security. Unable to locate him, officials were forced to put the entire facility on lockdown. About 10,000 people had to be evacuated, and everyone who’d already gone through security screening had to line up and get screened again.

There was a ripple effect, too — the incident caused hundreds of flight cancellations and delays at other airports coast to coast, according to the New York Times. The man was eventually arrested.

Yes, there’s no shortage of knuckleheads in airports — perhaps you’ve made a few silly mistakes yourself. But if there ever were a place to follow the rules and stay alert to your surrounds, this is it. Here are a couple of other tales of outrageous airport screw-ups, with some pretty good lessons for us all.

Weapons of trip destruction. One student flying to visit a graduate school got the second degree sooner than he expected — from the law. “I never packed a suitcase, just used the messenger bag that I carried around day to day,” he wrote on the news and opinion blog Jalopnik.com. Though he’d dumped out the bag and given it a shake before packing, that hadn’t dislodged a utility knife he’d previously tossed in for an art project. In fact, the knife had slipped into the bag lining, a fact the airport security screeners discovered as they scanned his carry-ons.

“I’m thinking, OK, nice work guys, you did your job, take the knife, I’m running late,” the student recalls. Instead, he was handed over to the airport police. “Arrested. Mug shot. Fingerprint. Summons.” With the help of an attorney, he got off relatively easy, with a $300 fine and six-month suspended sentence. The moral of the story? Always check your luggage thoroughly. TSA takes it job seriously — don’t assume they’ll laugh off a piece of contraband or believe you if you say you forgot it was there.

Related: 5 Way to Safeguard Your Luggage

From smack talk to perp walk. Steven Richey, who works in aviation safety, saw a little old lady get in big trouble for a bad attitude. “She had dropped something out of her purse and a TSA agent called out to her after he picked it up. She apparently didn’t hear him, so he walked over and tapped her on the shoulder,” he recalls. “She wheeled around and stuck her finger in this guy’s face,” and followed that up with a barrage of bad language and several racial slurs. If the woman assumed her tantrum would be tolerated because of her age, she learned differently in a hurry. “The last I saw of her,” says Richey, “she was being dragged away in handcuffs as all of the people at the checkpoint burst out clapping. Lesson: Don’t pick a fight with airport security unless you don’t want to get on your flight, or possibly any flight ever again.”

Trying to board after a few too many. Tabloids had a field day when one pop singer was barred from boarding a flight to the U.K. due to being visibly intoxicated. Not only did news of her bad behavior make headlines worldwide, she delayed the flight for an hour, inconveniencing everyone on it, as baggage handlers retrieved her luggage and returned it to her. She also got left behind by her band mates.

Committing a wardrobe malfunction. Sure, you should dress for comfort (and for running through the airport if you have a tight connection), but don’t dress to kill or suggest you might want to. Take the guy who was in a food line in front of Stephen Richey, who works in aviation safety, in the Orlando airport. “He was wearing a hat emblazoned with the word ‘BOMBER’ on it,” says Richey. “I later noticed an airport police officer following this guy.” Word to the wise: Don’t draw attention to yourself by wearing or carrying something that may look suspicious.

Packing explosive lookalikes. In 2015 a 15-year-old entered a Canadian airport with an alarm clock in his carry-on. The clock just happened to closely resemble a stick of dynamite with a count-down clock on the front. The bomb squad was called, and the boy was charged with mischief.

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Forgetting why you’re even there. Airport shops and restaurants can be hugely distracting when you have time to kill before you board — and some people miss their flights as a result. Andre Hinds, of Tulsa, Oklahoma, can vouch for that. “I would be in the [airport] coffee shop, find a newspaper and start poring over it, forgetting I had a flight coming out a few gates down the concourse,” he admits. “I once missed a flight entirely.” These days he sets an alarm on his smart phone to remind him when it’s time to head for the gate.

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