A retired NYPD lieutenant recently had a wild run-in with accused Long Island serial killer Rex Heuermann which “was like road rage without the car.”

Kevin Young said he had a “strange encounter” with the “intimidating bully” two weeks ago on a train into Manhattan from Massapequa Park, where they both live.

“We had a very innocuous interaction [where] he took umbrage to something that I was doing … and it just escalated into some heated words,” the ex-cop told the “The Ops Desk” podcast.

Young said he thought the confrontation was done — only for Heuermann, 59, to confront him again once they got off the train.

“We continued to [have] heated words” that only ended when Young walked away, he said.

“My impression was that he felt it was almost his right to be able to confront people and voice his opinion on whatever was going on around him, unsolicited,” the retired cop said.

“He’s physically intimidating,” he noted of the 6-foot-4 architect and dad of two, who was sensationally arrested a week ago in a police sting after being tracked for months and charged with three murders.

“I would speculate that he perhaps over the years has used his imposing size as a bit of an intimidation factor,” Young noted, saying Heuermann seemed taken aback at being challenged.

“I kind of thought he was a bully. He seemed to be the kind of person who felt he could get away with doing things because he was big and people weren’t going to say anything.”

Heuermann was charged the day after his arrest with murder in the deaths of Amber Lynn Costello, 27, Melissa Barthelemy, 24, and Megan Waterman, 22.

He has also been named the “prime suspect” in the death of Maureen Brainard-Barnes, 25. In court on July 14 he pleaded not guilty to all charges.

Young said he immediately knew it had been Heuermann on the train when he saw breaking news about the suspect, who’s been likened to an “ogre,” being arrested.

“He’s very unmistakable,” he said, saying he also recognized Heuermann’s “very distinctive” voice when he heard the now-viral interview he gave a year ago to a real estate YouTuber.

“I immediately recognized him as the person I ended computation with two weeks ago.”

Young said that while his run-in was not “pertinent to the case,” it gives “an insight into the kind of a mindset” he had.

Still, if not for Heuermann’s arrest last Thursday over the notorious Gilgo Beach serial killings, the ex-detective said he would’ve have brushed it aside.

“It was a bit odd,” he said of the run-in that “was almost like a road rage without the car.”

“But listen, this is New York — people do odd things all the time.”