The Danish New Year's Eve custom of smashing old plates against friends' doors is called plate-smashing.
In the tradition, people break unwanted or saved crockery outside the homes of friends and family. A large pile of fragments is considered a sign that the household has many loyal friends willing to visit and celebrate. The practice is associated with Danish New Year's festivities, although its popularity and form vary among families and communities.
The plates are generally old or otherwise no longer wanted, rather than valuable tableware. That detail matters because the custom is symbolic: the broken pieces represent friendship and good fortune, not destruction of household possessions for its own sake.
Denmark has several distinctive New Year's customs. These include eating kransekage, a ring-shaped marzipan cake, and watching the King's New Year address. Jumping from a chair at midnight is another Danish custom, but it is separate from plate-smashing.