For the last 25 years, Robert Dyer has lived a double life.

Every morning, he catches the 6 train at 7:40 a.m. to his city job at the Department of Health’s tuberculosis lab in Kip’s Bay where he preps specimens for testing.

At night, he loads up his pockets with cans of spray paint and blasts the buildings and bridges of Manhattan with his infamous “RD” mark.

The 49-year-old is one of New York City’s oldest and most prolific graffiti “artists” – spreading hundreds of thousands of tags over the span of 37 years.

“It’s like a drug, you get addicted to it,” Dyer told The Post, his 15-year old son at his side. “And I’m an adrenaline junkie.”

Two weeks ago, Dyer was collared outside his Upper East Side home and charged with 82 counts of making graffiti. The arrest capped a six-month investigation by 19th Precinct detectives who have regarded Dyer as a one-man quality-of-life blight for a decade, an NYPD source said.

Now, Dyer, who has 13 prior arrests, says he’s giving up doing graffiti in public places and on private property for good. But it’s not because he’s afraid of a 14th arrest.

“I don’t relate to the direction graffiti went,” said the Manhattan native. “It’s a bunch of soft yuppie hipster crap. The graffiti of my time is a long lost art.”

Dyer plans to continue splashing “RD” across retired city signs and canvasses to sell on E-Bay. His work fetches upwards of $3,000 because of his national

street cred.

He’s also tired of the gymnastics required of graffiti artists — climbing girders, sprinting from cops.

“I’m getting old and slow and I’m not as limber. Makes it impossible to do what I used to do,” he said.

Dyer was only 12 when he threw up his first tag on the inside of a 6 train at the urging of his older brother and friends. From that day in 1980, an obsession grew.

“I just wanted to get my name up as much and in as many places as possible,” said Dyer, who has RD tattooed on his right wrist.

In 1982, Dyer was arrested for the first time — painting a 6 train in the Bronx.

He bounced around several juvenile detention halls, eventually landing at Hawthorne Cedar Knolls High School for troubled youth.

He moved back to New York City after graduating and “kept messing around in the streets like an animal” throughout the 80s, he said.

“Bombing” the subways was his favorite.

Every night, Dyer would break into idle 4 and 6 trains, and scrawl his bubble RD tag on the outside of 100 cars a night, he said.

Some weekends, he’d decide to head to the Concourse Yard in the Bronx, where D trains were stored.

“I’d shoplift a bag of Fig Newtons and write Friday night to Sunday morning,” said Dyer. “I’d be covered in oil and dirt, but I just kept going.”

The single dad, who took an extended hiatus from graffiti in 2004 to focus on raising his son, said tagging was a coping mechanism.

“When tragedy strikes, I’d go ape s- -t,” he said. “It’s this comforting thing that I’ve consistently had in my life.

“My tag has out-lasted any relationship I’ve ever had,” Dyer said. “It will always be a part of me.”