"When we all came back together we found we'd all been harassed endlessly by quite angry older citizens who were joining this Christmas lunch.
"So it wasn't quite the lovely experience we expected. I think one of my flatmates basically got assaulted."
In her ninth-floor office in the Beehive and sat next to a decorated tree, the Prime Minister counted that day as her most disastrous Christmas and said while her friends probably all laugh about it now, at the time "it was particularly tragic".
This year Christmas looks set to be a lot less eventful as Ardern, her fiance Clarke Gayford and their daughter Neve will be heading to her hometown of Morrinsville in the Waikato where her parents still live.
Joining them this year will be her sister Louise with her family and on Christmas Eve they'll make "snowballs" - a tradition they've followed wherever they are in the world.
"Which are basically, if I'm honest, condensed milk and biscuits with marshmallows. It's delicious. And even when she was in London we would both make them wherever we were."
And Ardern is looking forward to making something more substantial on Christmas Day because she doesn't find much time to cook these days.
The Prime Minister is also looking forward to "the giving side" of Christmas and said the best gift she's ever given was sneakily making Gayford some fishing kit from some of his old Fish of the Day logos.
"I probably thought that was better than he did," said Ardern.
"But the best Christmas gifts for me is now just watching Neve get so excited with unwrapping things and everyone being together at the same time. That's really nice."
Now 2 years old, Neve is starting to understand the concept of Christmas but Ardern said one of the problems she and Gayford were running up against now was what to do about Santa's stocking.
The Ardern family's belief is Santa shouldn't be the one to get to give the decent presents so she usually found oranges in her stocking.
"I always thought Santa wasn't the great guy everyone made him out to be, based on that.
"So we're having a little bit of a discussion as to whether or not we're going to take this same philosophy with Neve. I think so. She's getting an orange."
Judith Collins
Judith Collins' Christmas wouldn't be Christmas without "Judith's World Famous Cheesecake".
"I've got to make it for my son and husband because it would be very bad if I didn't."
When Collins and her husband, David Wong-Tung, used to own a restaurant on Auckland's North Shore, she used to get up every morning at 6am to make the cheesecake before going to work at her law firm.
In an almost self-fulfilling prophecy, she marketed it as "world-famous" then it became a bestseller.
The secret is the rum in the topping.
"People wonder why they really like that topping."
Collins used to be able to make the cheesecake in the dark.
"I thought I know when I'm over having restaurants when I forget how to make that cheesecake. I haven't yet forgotten."
Collins will spend Christmas with her family in her Papakura home and, besides the cheesecake, will be making duck and lamb.
"I have this sort of aversion to poultry so I will probably cook lamb or something like that. It's very hard to go past good New Zealand lamb with some rosemary and things."
She told the Herald she's really looking forward to spending some valuable time at home after spending so much of it on the road for the election campaign after being elected leader in July when Todd Muller stood down for mental health reasons.
"It's been an enormous year and certainly the second half was entirely not what I'd ever envisaged because I basically was very happy being the MP for Papakura and writing my book," Collins said.
"So [it's been] entirely different but I have to say I've been really enjoying being Leader of the Opposition."
