JOE DeFELICE, a lifelong Mayfair man, was driving around his neighborhood when he saw that the guy who rented an apartment above Jean's Pizza, at Ryan and Rowland avenues, had hung out a big yellow banner that read, "WE BUY HOUSES FOR CASH" and included a phone number.

DeFelice was outraged.

"I called the guy up and I said, 'Hey, man, that banner looks horrible. You think you could take it down?' Guy said, 'Who [the hell] are you?' I told him I'm president of the Mayfair Civic Association and the Mayfair CDC. He said, 'The neighborhood's a s--hole anyway.' And he hung up."

DeFelice reached for his smartphone and first-term City Councilman Bobby Henon's free CityHall App, a wildly popular weapon in Henon's "Bad Neighbor Initiative" against landlords and tenants who blight their blocks.

"I take a picture of the banner and throw it up on Bobby's app," DeFelice said, "and I tell people, 'This guy [is disrespecting our neighborhood] - here's his phone number.'

"Next day, the banner is gone and the guy calls me and says,'I'm so sorry. I didn't realize who you were. I'm getting hundreds of angry phone calls and texts. Look, man, just make it stop.' "

DeFelice, a high-energy lawyer who has reported dozens of nuisance properties, said that Henon's app "has put a level of shame on bad neighbors."

"And the shame game works," he said. "The days of knocking on someone's door and asking them to clean it up are over because if you say, 'Hey, man, your place looks like s---,' they might punch you in the mouth."

Henon, who introduced his CityHall App last spring and quickly saw hundreds of Northeast residents download and use it, discovered that when property violations go viral, most offenders cave. If they don't, he'll summon them to public hearings and alert Licenses & Inspections - which is never good news for a noncomplying city property owner.

Anthony Cancelliere responded immediately after Henon called him out publicly for $24,449 in tax delinquency on two of his dozens of Northeast properties, and 106 code violations that generated 38 neighbor complaints.

"I'm really glad this happened because I had no clue," Cancelliere told the Daily News. "I'm a Mayfair guy, not somebody who lives in Jersey. My office is a block away from the councilman's. I called him right away. I paid the taxes.

"I don't have abandoned houses with broken windows. I don't do Section 8. Most of the violations were for things like high grass. The tenants are supposed to cut the lawn. And for things like loud music - I got rid of that tenant."

Henon said that Cancelliere's quick response and willingness to cooperate is how the Bad Neighbor Initiative is supposed to work.

"Take a picture, write it up, send it in on my app," said Henon, whose boots-on-the-ground style brings him face to face with neighbors good and bad during his district walks, and whose CityHall App has gone so viral that he's getting pothole and tall-weeds complaints from France, as well as from around the corner. He addresses Northeast complaints quickly. France, he can't help.

"Sending a real-time photo and information is revolutionary," said the city's appreciative L&I commissioner, Carlton Williams. "Henon is taking it to the neighborhoods, providing people with the tools and the access to be the eyes and ears for reporting nuisance properties.

"We have 63 inspectors to enforce all the codes for 550,000 single-family residences plus businesses and apartment buildings," he said. "We need those eyes and ears in the neighborhoods."

Williams said that he and Henon are working to "marry" the councilman's CityHall App to L&I's new website, which puts any address' history of violations in the hands of citizens reporting nuisance properties.

Talk about transparency. Together, Henon's app and L&I's new website demolish decades of good-neighbor frustration over trying to hold bad neighbors accountable.

This fall, Henon plans to summon landlords like Walter Ulatowski to a Council "Bad Neighbor" public hearing in the Northeast.

Henon targeted Ulatowski, who owns 86 properties in Henon's district, after finding 13 with expired housing-inspection licenses, 15 that never had housing-inspection licenses, 399 code violations, 171 citizen complaints to the councilman's office and a $3,438 tax delinquency.

Henon said he wrote to Ulatowski, telling him to clean up his act or be publicly targeted. Ulatowski did not respond. His day in front of Council approaches.

Besides landlords, Henon also targets problem owner/occupants. When Henon learned of the neighbors' eight-year struggle with an owner/occupant on Chippendale Street between Crispin and Leon who was a hoarder and whose house was infested with bugs, he had L&I get a court order to clean out the house and offer the occupant social services.

The owner of a property on Charles Street between Comly and Creston was collecting rent despite dysfunctional appliances and a leaking roof. Henon told the tenant to stop paying rent, then told the owner why. The problems were quickly resolved.

On Vista Street between Rowland Avenue and Crispin Street, neighbors complained about drinking and drugs at a nuisance property. Henon said that he would personally get the District Attorney involved if the owner didn't clean up his act. Suddenly, the complaints ended.

When he's not personally pursuing Bad Neighbors, Henon is working on a program that will target tax delinquents the way his app targets nuisance property owners. Often, he said, they are one and the same.

And he's identifying nuisance properties that might qualify for state Rep. John Taylor's Act 135, which allows a community development corporation (CDC) to take conservatorship of a nuisance property, fix it up and bill the owner for repairs.

If the owner fails to pay, the CDC can sell the property, recoup its repair costs and give the rest to the original owner.

The Mayfair CDC is testing Act 135 in the courts for a longtime nuisance property on Sheffield Avenue near Frankford Avenue in Henon's district.

"This property's been boarded up for at least seven years," said Joe DeFelice, the CDC's president. "In Mayfair, you hardly ever see boarded-up houses. The owner painted the boards to look like window shades but when they came loose, birds were flying in and out of there all the time. It was like a big nest. The next door neighbor was afraid to let his children play on his own front lawn because of the rats next door."

The owner has been nonresponsive, DeFelice said. So the Mayfair CDC wants to take over the house, fix it and sell it - making the block whole again.

Henon is watching the case closely. If the Mayfair CDC succeeds, he's already got eight chronic-nuisance properties targeted for the Act 135 process.

Blight never sleeps. Neither does Henon.