Officer Joe Rivera, a member of one of Suffolk Police Department’s two anti-gang units, grew up on Manhattan’s mean streets.

“You move forward and you move on with life, but you never forget,” he told John F. Kennedy Middle School students Friday.

Rivera and Suffolk prosecutor Nicole Belote, who specialize in busting juvenile gang members, spoke at the school during a presentation by the Suffolk Commonwealth’s Attorney’s Office.

Rivera told of heroin addicts chasing him for his lunch money and of gang leaders trying to recruit him.

He always had an excuse, he said. Music practice, dancing or boxing commitments — he had someplace else to be, he’d tell the thugs.

“I joined the NET (Neighborhood Enforcement Team) partly to lock people up, but that’s not the part I enjoy,” he said. Helping youths stay out of gangs is his favorite pastime.

Students who see the presentation, featuring two videos in which former and inactive gang members share their stories, come away with plenty of reasons to keep out of trouble.

“The Big Lie: Unmasking the Truth Behind Gangs,” includes testimony from one ex-gang member who was shot and put in a wheelchair for the rest of his life at age 18. Interviewees say they joined gangs because their lives lacked a male role model.

Father in prison, abusive family members, parents abusing drugs — these are among the main reasons vulnerable youth find false comfort in gangs, students were told.

“If you join a gang, there are three places you will end up: prison, hospital or dead,” Belote cautioned.

Suffolk students will continue to be shown the presentation and its graphic videos, containing a gruesome slideshow of gang members dead on street corners and footage of drug-crazed gangsters firing pistols into the air, until they get the message, she said.

“You’re still getting arrested,” Belote said. “You will all quit seeing these videos when we quit seeing you.”

In the second video, “Gangs In Suffolk” — locally produced — ex-gang member Zavier Thompson, an obviously intelligent and articulate young man, tells of his gang experiences including drug abuse and violence.

“I think it clouded my judgment because it made me think I was living a good life, living a rock-star life,” he tells the camera.

“Everybody on the street has an expiration date,” Rivera warned students. “If I don’t get you, a bullet’s going to get you.”

Teens with gang concerns should reach out to a family member, pastor, teacher or other responsible adult, Rivera said, adding that he can be called at 514-7860.