In a Danish New Year's Eve tradition, people traditionally smash plates against friends' or neighbors' doors.
The practice is often described as a way to show affection and bring good luck. A household with a large pile of broken crockery outside its door is traditionally understood to have many friends who visited to wish its occupants well. The custom turns an otherwise ordinary object into a symbolic New Year's gift.
The tradition is associated with Denmark's broader collection of festive New Year's customs, which can include jumping from a chair at midnight to “jump” into the new year. Fireworks, parties, and the Danish New Year's speech are also prominent parts of the holiday.
Descriptions of plate-smashing vary by source and by household. It is a folk custom rather than a compulsory national ceremony, and modern celebrants may avoid it because of noise, waste, safety, or property concerns. The item is specifically plates in the conventional account, not the champagne glasses often associated with New Year's toasts in other countries.