Within the last month, one customer asked for a Russian flag, he said, just for the sake of burning it.
The opposite was true for Algeria. The day before that country's Tuesday evening game against Belgium, a dozen Philadelphia fans of the North African country's team suddenly wanted its green, white, and red star and crescent in all sizes.
"That was kind of shocking," O'Connor said. "This is the biggest push for Algerian flags that we've had."
To keep up with demand, he had to have his Pottstown factory make them overnight.
The store saw a decline in Spanish flag sales after the country's 2-0 loss to Chile on Wednesday.
"Most people were really expecting Spain to go further," O'Connor said.
Upon entering Humphrys, which is 150 years old this year, customers see a rainbow of flags strung on a rope and hung wall to wall, historic American flags serving as tapestries and curtains, bouquets of miniature flags, canvas paintings of flags.
On a shelf near the back of the store, boxes of country flags sit alphabetized, from Afghanistan to Zimbabwe. O'Connor likes to keep one of each in his store at all times, as he never knows who might stop in.
At Humphrys, across from the Betsy Ross House on Arch Street, World Cup fans can find banners they use as capes and scarves and fly in sports bars or on couches to support their countries of choice.
In the Pottstown factory, 17 employees sew national emblems on fabric sizes ranging from 12 inches by 18 inches to 50 feet by 80 feet. Most flags cost between $27 and $80.
Leading up to the Cup, the company's top sellers typically included Italian, Croatian, South Korean, United Kingdom, and Nigerian flags. There's been a run on the last lately - O'Connor attributes that to supporters of Boko Haram kidnapping victims in that country.
So far, Greek and Dutch flags have sold surprisingly little during the tournament, O'Connor said.
Even when the World Cup is not being contested, Humphrys can rely on the support of soccer fans.
Sons of Ben, the group that roots rabidly for the Philadelphia Union, is a longtime client of Humphrys. For Major League Soccer games, the Sons fly flags they've bought of their players' home countries, such as Sierra Leone, Brazil, Mexico, France and Argentina.
Though most of the 2,200 Sons of Ben will be shouting "U.S.A." on Sunday, some support France, the Netherlands and England - rather, some did support England. Its chances ended Friday with Italy's loss.
"Everyone has his own affiliation," said Sons of Ben president Kenny Hanson, who expects to watch the United States-Portugal game at Fado in Center City.
Hanson doesn't need to buy any flags for that match. He already has plenty of the Stars and Stripes.
"I'm very optimistic for Sunday's game," he said. "I'm very confident that they can pull out a win against Portugal."