They flock to Hackensack from miles around for a taste of the barbecued pork and other all-American fare served by Robert Egan at Cubby’s, his restaurant in northern New Jersey.

Some of them flock from as far away as Pyongyang. The North Korean ambassador to the United Nations was at Cubby’s a few days ago, engaging in what may be the world’s most improbable diplomatic tango with a self-appointed American negotiator whose main claim to fame is his spicy barbecue sauce.

For almost 15 years, North Korean diplomats have been eating with the Henry Kissinger of burger joints. “Condoleezza Rice [the US secretary of state] made a speech a couple of weeks ago about the conditions that needed to be met before this or that could happen between America and North Korea,” Egan, 50, said.

“Now I’m a pretty smart guy,” he continued, “and I didn’t know what the f*** she was talking about. The bottom line is that this administration wants nothing to do with North Korea.” That is perturbing to Egan, who stumbled into a unique relationship with Pyongyang through his efforts to find US soldiers missing since the Vietnam war.

With his profanity-laced “Noo Joisey” way of speaking, Egan seems the unlikeliest candidate for sensitive diplomatic negotiations with the notoriously erratic North Koreans. Yet after several trips to Pyongyang in pursuit of missing American soldiers, invitations were issued to North Korean officials to try some real American food at Cubby’s.

One of those officials was Han Song-ryol, who not only became North Korea’s UN ambassador – and a regular visitor to Cubby’s – but subsequently acquired a new set of all-American teeth, thanks to John Kallis, a friend of Egan’s who is an oral surgeon. “Bobby called me and said, ‘You’ve got to do me a favour’,” Kallis recalled last week. Han had severe toothache, but was wary of submitting to American healthcare. Yet the ambassador trusted Egan enough to undergo a general anaesthetic while Kallis extracted 12 teeth and inserted 13 implants.

Exactly what Egan may have achieved with all of his Korean rib-tickling is hotly debated in diplomatic circles. Egan claims that it was through his relationships that Pyongyang drew back from confrontation three years ago over its illegal nuclear weapons programme.

Several US officials have publicly praised his efforts to keep a channel of communication open; others see him as a dangerous maverick who sometimes subverts US government policy.

Egan snorts with derision at the “boycott brigade” who refuse to negotiate with North Korea. “The fact is, it’s no longer the hermit kingdom,” he said. “It’s no longer the only dark hole in US intelligence. There’s me, and I’ve been there and I know them. How can you turn your back on that?”

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