"In fact, several of my friends are 'over' the ukulele," he says. "They feel like it's been a little overexposed. But you can't deny it's a very joyous instrument."
One key reason for the instrument's rising popularity is the appeal it holds for children as an introduction to the world of music.
"When I was at school it was all about the recorder and I definitely think the ukulele is a huge leap forward. Being able to sing along, and sing in a group, and accompany yourself, is such an amazing feeling."
The trust is all about helping to provide instruments, resources and knowledge, to schools and communities, including teaching interested teachers how to play the ukulele so they can pass it on to their classes.
"It's great because there are teachers out there who thought they wouldn't be any good at music, but they've picked up the ukulele and embraced it and now they're rock stars in their own schools."
As for his own two young children, he hasn't forced the instrument on them just yet.
"I've got a few ukuleles around the house, but we'll just see if they pick them up. They're pretty little."
Those ukuleles have a serious purpose too - they do get used while McKenzie is composing new material. The Academy Award winning-writer is now finishing the songs for the next Muppet film, Muppets Most Wanted, which stars Ricky Gervais and Tina Fey.
"On Monday I was in the studio with Kermit, recording his song, which was a lot of fun. And next week we'll go into a studio and have an entire orchestra playing along to my songs, which is just one of the coolest things I've got to do."
Writing a song for Gervais also proved very rewarding. "So it turns out Ricky Gervais was a pop star in the 80s so he's a great singer. They were called Seona Dancing. It was this almost Bowie-style band, a new romantics band, and he was the lead singer. It's kind of amazing, because he looks so young and thin."
The most imminent piece of McKenzie's work that Kiwis can see is his role in Austenland, an off-beat addition to the oeuvre of film-maker Jerusha Hess, who co-wrote and directed Napoleon Dynamite and Gentlemen Broncos with her husband, Jared. It tells the tale of an American woman obsessed with the works of Jane Austen, who goes to a boutique Austen-themed fantasy getaway weekend, where she intends to have a romantic encounter with a Mr Darcy type.
"It's my rom-com debut," he says. "I don't know if I'll get to do another one but it's a really fun, kooky rom-com, one of the most kooky you're ever likely to see. It hasn't done great with the critics, but I think they were expecting something more literary, and instead it's really this kind of hilarious romp. It's about crazy fandom and it's a very broad comedy."
"The servants around the grounds, for example, the guards and butlers, they're all very well-endowed, with socks down their lederhosen, or whatever they're called, breeches, pantaloons. But it's hilarious, they look sort of like porn-star judges. And Jennifer Coolidge, who is always brilliant, is just wildly out of control, which was great to watch."
Though he's clearly enjoying the acting opportunities coming his way, McKenzie's next project will see him back in the writer's chair - he's currently working on developing a new fairy tale comedic, Labyrinth-style musical film, with some help from fellow Flight Of The Conchords writer James Bobin. Think singing dragons and mythical creatures mixed with live-action and music.
"We're in pre-production, so it's early days, script stage really. But yeah, having learned so much working on The Muppets I'm excited about working in a world where we get to create everything afresh. It's been a busy year, but I'm looking forward to having some time to work on it."
Who: Bret McKenzie
What: Recently announced as Ambassador for the New Zealand Ukulele Trust, and soon appearing in new film Austenland
When and where: Austenland is in cinemas from October 17, and the NZ Ukulele Festival will take place in Auckland on November 30
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- TimeOut