Is it possible to duplicate an item?

During some events, I got some rare items that seem limited to said events. But, I want to use more than just the few of them I obtained in decorating my home. Is there a way duplicate items in Animal Crossing:New Leaf?

Yes, it is possible to duplicate items, but only items that can be dropped on the ground.

That being said, I advise against doing it, because messing up the timing can corrupt your save file (making it unplayable) and it's obviously considered cheating.

If you decide to duplicate items anyway, here's how:

1. Go to a friend's town via local or internet connection.
2. While outside, drop the item(s) you wish to duplicate on the ground
3. Have your friend choose 'End your multiplayer session.'
4. The game will show that you are leaving, then the save screen will pop up. There is a small icon in the lower right corner during the save screen depicting a circle. It will rotate, starting at the top of the circle. Let the circle rotate once, then hit the wireless switch on the side of your 3DS. It's a small window to hit, so if you are too fast or slow, you risk not having the glitch work correctly.
5. You should see an error screen with Mr. Resetti on it. You should then arrive back in your town with the item(s) still in your inventory, and they should also still be on the ground in your friend's town.

Sources: IGN guide, solidus snake777's GameFAQ