A former Cantor Fitzgerald partner who nearly died on 9/11 has had another trauma to deal with — a downstairs neighbor from hell, according to a Manhattan lawsuit.

New York Times-bestselling author Lauren Manning and her husband are suing the landlord of their former Park Avenue pad after the building sided with the rent-stabilized tenant in a noise dispute — even though he was caught on camera barging into their $12,000-a-month apartment screaming obscenities

“I’m a wacko, man, I’m f—ing crazy!” Kenneth Finkel yells in the video, which is referenced in the couple’s new Manhattan Supreme Court lawsuit.

Manning and her husband Gregory say they were driven from their pad because their landlord, the Rudin Management Company, did nothing to address the “wacko.”

“You’re dealing with the wrong one, man,” Finkel continues in the video. “Forty-two years I’ve been in this building. I pay $650 a month for my apartment bro, OK? $650 a month, OK?” he boasts.

“You like the music?” Finkel asks, apparently referring to tunes he had been allegedly blasting through their floorboards.

“I hope you do, because it’s going to be it so f—ing loud!” he screams.

Finkel pleaded guilty to criminal trespass in the second degree over the incident earlier this month and is awaiting sentencing, according to court records.

He told The Post on Friday that he blames the dispute on the Mannings’ 14-year-old son, who he claims first began playing music really loudly.

Finkel admits to playing Frank Sinatra in response in his seventh floor unit at 1085 Park Ave. on East 88th Street.

“They’re just f—ed up people, man,” he told The Post.

But according to the couple’s suit, soon after the Mannings moved into No. 8C in 2014, Finkel, who lives in No. 7C, began a campaign of “harassment.”

First, Finkel repeatedly rang their doorbell until Lauren Manning answered, the suit says. Then he demanded to know “Who are you?” according to court papers.

He soon began yelling “belligerently at Lauren” about noise coming from her son’s bedroom, the suit says.

Lauren Manning, who was badly burned in the WTC attacks, filmed Finkel when he forced his way into their apartment on Dec. 8, 2015, the suit says.

His screaming tirade about being a “wacko” caused Lauren Manning to burst into tears.

“You should be crying,” Finkel shouts in response.

The cops eventually arrested Finkel, but executives from the family-run Rudin Management Company refused to take action against their unruly tenant, the suit says.

The Mannings’ lawyer, Neil Brickman, said his clients believe that Rudin didn’t take action in retaliation for them making general complaints about their rental.

In the video, the long-time renter brags, “You can call Rudin, I’m best friends with Rudin, man.”

Because the Rudins allegedly refused to deal with Finkel, the Mannings were forced to leave the building, their suit says.

“We found a new place and we’re very happy here,” Gregory Manning said.

A Rudin family spokeswoman said, “We believe that the claims in this lawsuit are completely groundless and have no merit, and we will seek to have it dismissed.”