En route to the University of Colorado on Tuesday evening, President Barack Obama made an unexpected stop at The Sink, the venerable low-ceilinged pub on University Hill, where tables full of unsuspecting, mostly college-aged customers munched on burgers and fries.

Obama’s motorcade peeled off BroadwAay on to 13th Street around 6:30 p.m. and pulled up in front of the bar. People in the street erupted in cheers as they realized who had just arrived, and Obama shook hands with surprised patrons dining on tables out on the sidewalk.

A young woman who the president approached inside The Sink told him she wanted to open a shop that sells cheese fries. He congratulated her before adding a rejoinder.

“And it sounds low-calorie also,” Obama said. He added, with a smile, “We’ll be on the lookout.”

The president also spoke with a man from Australia who was sitting with a young woman he told Obama he was still attempting to woo.

“Smart guy,” Obama told him.

Outside the pub, the president received perhaps a little more love than he planned to. A young woman holding a yogurt snack promptly dumped it on the ground as Obama walked by, splashing some of the purple liquid onto the president’s trousers.

Obama wiped at his pants a few times, but took the accident in stride as the woman told him how embarrassed she was.

“Getting yogurt on the president, that’s a good story,” Obama said.

The president also ran into a budding entrepreneur in the crowd outside — a young man who showed the president a smartphone app called Sphero that could remotely pilot a ball around.

Obama took the man’s phone and in just a few seconds guided a blue, luminescent ball along the sidewalk for a few feet.

“That’s terrific,” the president said. “Good luck to you guys.”

After the president turned in the middle of the intersection of Pennsylvania Avenue and 13th Street to wave at the sizable crowd, he was hustled by Secret Service agents back into the presidential vehicle for the short ride to the Coors Events Center.

The president’s stop at The Sink came as a surprise to the longtime Hill burger joint’s owners and its 40 to 50 patrons, co-owner Mark Heinritz said later Tuesday night.

“We found out about 20 minutes or so before he showed up,” he said.

In that time, the Secret Service came in the restaurant, did the necessary security sweeps and strung yellow caution tape outside the restaurant. The patrons who were in the restaurant were allowed to stay.

Obama shook everybody’s hand and spent about 30 seconds with each person in the restaurant, Heinritz said.

“He really just seemed like a nice approachable guy,” he said.

Heinritz gave some Sink T-shirts and hats to Obama to give to his family, and his staff crafted a Sinkza — a pepperoni, sausage, green pepper, black olives and onion pizza. The president, in turn, left a mark of his own at the Boulder restaurant.

He took a black Sharpee to the restaurant’s low ceiling and signed his name next to “Diners, Drive-ins and Dives” host Guy Fieri’s sketch.

Camera Business Writer Alicia Wallace contributed to this report.