The PM was chomping on the Â£1.80 snack on an Easyjet flight to Portugal - sparking incredulity on social media.
Fellow passenger Ashleigh was amazed too, telling her Twitter followers: "Guys I'm crying he was eating Pringles."
"I found the experience humbling," she told BBC News.
The eagle-eyed teenager also managed to grab a selfie with the apparently oblivious Mr Cameron to liven up the holiday flight she was taking with her boyfriend.
The prime minister, who was sitting with his bodyguards, can be seen playing with - or possibly working on - his iPad in an economy seat.
He is believed to have been flying out to Portugal to join wife Samantha and their three children on holiday.
Twitter users were quick to flag up other examples of snack-related Cameron trivia - such as a curious picture of him eating a hot dog with a knife and fork during the election campaign.
Others wondered why the prime minister was using a budget airline, suggesting he was trying to burnish his "man of the people" credentials.
Britain's political leaders have been wary of being pictured eating since then Labour leader Ed Miliband was snapped by a press photographer having difficulties with a bacon sandwich.
Why do politicians try so hard to eat like voters?

At a campaign rally, he called the South Carolina senator an "idiot" and then told the crowd to try the number.
A Politico reporter called the number on Tuesday, and Mr Graham answered.
Mr Graham recently called Mr Trump "a jackass" and condemned the real estate mogul's comments about Senator John McCain.
Mr Trump has come under increasing criticism from fellow Republicans and veterans groups after he appeared to disparage Mr McCain's war record.
"He's a war hero because he was captured. I like people who weren't captured," he said, referring to Mr McCain's time as a prisoner of war in Vietnam.
Recent national polls show Mr Trump with a double-digit lead over his closest Republican rival.
However the polling was mostly conducted before the controversial comments about Mr McCain.
His rivals are becoming increasingly frustrated as Mr Trump continues to dominate the media coverage of the crowded Republican race.
Mr Trump has drawn headlines since he called undocumented Mexican immigrants "rapists" and "criminals" when he launched his campaign in June.
"The world is literally falling apartâ€¦ and all we're talking about is Donald Trump," Mr Graham told CNN on Monday.
To question the military record of Senator John McCain, a former prisoner of war tortured so brutally that he is unable still to raise his arms above his shoulders, would ordinarily have been suicidal.
But Trump is operating under rules of his own making that are perfectly suited to the voracious metabolism of the modern media, and the hyperventilated style of modern campaigning.
The more outrageous his remarks, the more coverage and social media comment he generates. And the more coverage he receives, the better his polling numbers seemingly become.
Increasingly, notoriety equals popularity amongst a large cohort of Republican voters.
Trump: Master of the demolition derby

Officers from Police Scotland alerted Benbecula Community Council to the scam at a meeting of the council earlier this week.
Sent from Italy, the email involves a fake story about an African man trying to transfer his inheritance to a new account after his father was poisoned.
The use of Gaelic in the email is poor, according to speakers on the isles.
Benbecula Community Council believed the email may have been written using online tool, Google Translate.
Scots Gaelic was added to the service in February this year.
A teenage girl has added a new chapter to the politicians-eating-things file after filming David Cameron tucking into a tube of paprika Pringles.
[NEXT_CONCEPT]
US presidential candidate Donald Trump has given out the mobile phone number of Senator Lindsey Graham - one of his Republican rivals for the White House.
[NEXT_CONCEPT]
What is believed to be the first email scam using Gaelic has been targeted at residents of the Western Isles.