He was an undercover NYPD narc who busted 500 dealers. Now he wants to be a judge.

Now he wants to take a crack at the bench.A Staten Island civil judge candidate has a wild, action-packed past as an undercover narc who posed as a dope fiend to bust dealers in NYC back in the 1980s.Glenn Yost told The Post he made more than 500 drug busts with the NYPD – including the very first grand jury crack-sale case on Staten Island. “I feel like I’ve come full circle in the law – enforcing it for 20 years, teaching it, and practicing it for nearly 20 years,” said the 63-year-old Republican lawyer.Yost was born in Brooklyn and moved to Staten Island when he was 11 years old.

He was raised by a single mother who worked at Sears.He was 20 years old when he joined the NYPD and became part of the narcotics unit two years into his career, he said.He ran undercover operations for the NYPD in Brooklyn, Manhattan and Staten Island under an alias.Deep undercover, he lived in a wiretapped apartment in Brooklyn and had fake ID and credit cards.He assumed new identities like “Vinnie” – a red Eldorado Cadillac-driving aspiring actor who summered in the Hamptons, but hung out in squalor-filled crack houses to score heroin, cocaine and prescription pain med Percocet.“Those shooting galleries, if there’s anything you can imagine close to hell, that would be it,” he said.“It was scary because you didn’t know, you didn’t know who was who.

You didn’t know if you were going to get robbed.It smelled horrible.

People would go to the bathroom wherever they wanted to.”Consistency helped him gain the dealers’ trust — so he became a repeat customer.A confidential informant helped cement the relationships.“I think ideally what the undercover needs to be is very clever and cunning,” Yost said.Sometimes, he was forced at gunpoint to sample the drugs to prove he wasn’t a cop.

But Yost mastered the art of pretending to sample the goods by dipping his forefinger in the powder — but bringing his middle finger to his mouth.Dealers, he said, ...