With every release of Animal Crossing, there is expected to be a number of glitches and easter eggs in the game itself. While many easter eggs have been found, this glitch is not very well known to many users, especially outside of Japan.

For this glitch, which is definitely not a hack or a cheat, you need a Tweeter. Remember those things at Birthday parties, where you blow into the one end and the other end fills with air and sticks out? That is the item, and is difficult to obtain for some. Streetpassing one person multiple times in Animal Crossing New Leaf rewards you with gifts from the visitors. These gifts range from balloons to food, and a Tweeter is one of the randomly given items.
With Tweeter in hand, head to a town with at least one other player, with a tweeter per person (You can share one, but it's more fun with 4 players where everyone has one). The person should face a large item; I like the train tracks or the river. Dig 2 holes on both side of the player. It could look like this:

xxxxx
o p o

Where x is the object, p is the person, and the o's are holes. Then, they face the object and repeadtly tap A.
Another player comes up behind them and 'pushes' them towards the object (while the other taps A). To do this, simply walk towards them. The person will work their way onto the object and be, well, in or on it.
Train tracks are fun to explore, as are the rivers, public work projects and buildings. To leave the glitch zone, there are different ways. Many you can step out. For train tracks, head to the steps to the Main Street, and walk down. But some places have no way to leave, like Cliffs. In this case, the player must end the multiplayer session.

We hope you enjoy using this glitch, and we will soon be sharing some images of our antics with it in places like Bonfires, swimming in clothes, and catching fish while standing in the river.

[Thanks to TyHarvest for the tip. Thanks to Ruceyod, RedPanda, DeviousSnorlax and Groose_Lord for helping out.]