"They're just going gang-busters. It's just ridiculous."
Mr Duke had no explanation for the shorts' sudden popularity - he could only say they'd become "a real cult item".
He said they'd become "huge" about Christmas time.
But budgie smuggler sales were still holding steady.
"Look, they'll be around for a very, very, very long time, but in terms of something that has really gone off, it's those NRL shorts."
The Herald observed at Takapuna beach this week that NRL shorts were very much a young man's game, though most still favoured the classic board-short.
Budgie smugglers were reserved for men of a certain age who had grown out of shame. They were often paired with an open shirt and grey chest hair.
Undoubtedly the youngest person at the beach rocking a pair of the revealing swimwear was Andy van Lier, 49, who was smooth-chested and shirt-free.
When asked why he chose to wear the banana hammock, the Ellerslie man said: "Because I can get away with it."
Mr van Lier, who gets told by his teenager to keep the budgie smugglers on the beach, said he hadn't really noticed anyone else wearing the same swimwear as him.
"I'm more of a bikini watcher."
Further down the beach, Stu McGlashon, 38, wore an impromptu pair of speedos - his green Jockey underwear. "It was a random decision to come to the beach," he said.
But living a day in another man's style of swimwear hadn't convinced him to convert. At heart, he's a boardie man through and through.
Mr McGlashon, of Mt Albert, has a pair of budgie smugglers at home from his swimming days, but hates them. "They're too revealing."
Having too much skin on show is also the reason Chris Kirten, 29, chooses board-shorts over anything else. "It's good to keep them guessing," the Ellerslie man said.
"You don't want to give too much away."
Mr Kirten also isn't a fan of the swimwear of the summer, NRL shorts, as they're a little too skimpy and he doesn't play league.