It is funny what you absorb by living in a different country, without even trying. You use expressions you've heard and used for years and everyone understands you, then you move to another country and meet new people who sometimes have no idea what you are talking about.
For instance, I was chatting to a friend and mentioned that we are Flat Stick at the moment. What is flat stick? she asked. Obviously an unknown expression on this side of the world, it means you are very busy and usually too busy to do other things you'd like to do. Flat Stick and Flat Tack are interchangeable.
While visiting a friend in the village, during our chat she made me laugh so much I said "You're a Dag". On seeing her puzzled face I had to explain, no this does not have anything to do with something hanging from the back end of a sheep (one of the 20 million or so woolly animals which populate the countryside in NZ), but it means you are funny in a nice way. I could have also said she was Hard Case, which also means - makes you laugh. After researching the dag expression I found the Australians use it with a different meaning - to dress badly - that is, not in fashion, or rather in bad fashion.
Years ago in NZ there was an entertainer/comedian, Fred Dagg (aka John Clarke, who is actually Australian). He had a show with sketches, songs and the like and his trademark dress was a floppy hat, black singlet and gumboots. A black singlet is the kiwi icon of sheep shearers. He also had a hit called If it Weren't For Your Gumboots, the UK version used Wellies instead of Gumboots. You have to wonder if the kiwi version of dag was in any way influenced by Fred Dagg, being a comedian. Rattle Your Dags means get a move on, or shake a leg.
If you travel around NZ you might like to take a Tiki Tour (or Cook's Tour), which is take a trip the long or roundabout way rather than the most direct route. It's often used if you are not sure where you are - you tell people you're on a tiki tour (lost) but eventually you find your way back to the main road. Unless someone puts you Crook - gives you wrong directions or information - then you could end up in the Wopwops (usually the countryside - you see noone and there are no landmarks in sight). If you really do get lost you could be Up the Creek Without a Paddle (in trouble).
While you visit the wopwops you might need to use a Longdrop. This is a primitive toilet which is usually a hole in the ground (which drops a long way) and if you are lucky, you have the luxury of a seat and perhaps 4 walls, but little else.
Your neighbour might invite you over for a Barbie, which is a barbecue. And if you're asked to Bring a Plate, you should put some food on it for sharing with the others who will be at the barbie. You could take it along in the Chilly Bin (cool bin, plastic food store) because if you just turn up with an empty plate they might think you are a Sandwich Short of a Picnic (not very bright).
The next day at work at Smoko (morning tea, or coffee break) you can tell your host what a lovely time you had at the barbie and invite him over to your place for the next one. If he says Cool Bananas or Good On Ya Mate, then it's all ok and you are well on your way to understanding kiwi slang. He might also say, come over later and I'll Shout You one - this will be a beer and he is paying.
After that you should go home and find your Togs (bathing suit) in case there is time for a swim, Jandals (flipflops/thongs), buy a few Mystery Bags (sausages) from the Local Dairy (corner shop) and when your partner asks for some help with getting it all ready, you don't have to Bust a Gut (make an effort), just say She'll be Right!