Revellers in more than 300 cities have gathered for the annual Santacon party - a mass gathering of people dressed as Santa Claus, partying in the streets.
Santacon, which began in San Francisco in 1994, has become a huge event across the world - a strange mix of a party, flash mob, pub crawl and mass carol singing service.
In London, thousands of Santas converged near Russell Square on Saturday after separate marches through the east, west, north and south of the city. Fortunately, word had got out on the Santa grapevine to avoid Trafalgar Square, the usual assembly point, due to the rather more sober vigil for Nelson Mandela being held there.
London's Santacon passed off without incident, but in recent years the Santacon movement has prompted a backlash from city dwellers and bar owners fed up with the antics of drunken, boozy Santas.
This year the event's organisers vowed to "clean up Santa's act". It posted several notices on the Twitter account of the movement's London branch, warning Santas to be careful and vigilant when using public transport, avoid public drunkenness and littering, and to respect the law.
The organisers of the London event encouraged attendees to avoid "giving Santacon a bad rep". "Santacon is about spreading goodwill and cheer, not being antisocial. Be Jolly! Be merry! Enjoy the surreal silliness of 1,000 Santas thronging the streets of London. But make sure your merriment doesn't end up causing grief for others. Bad behaviour such as leaving litter, acting drunk and climbing on things is the opposite of spreading goodwill, and giving Santacon a bad rep makes it harder to put on in future years. Keep an eye on your fellow Santa and if you see a Santa being rowdy, get them to calm down.
"Be sensible about alcohol. Babysitting Santa while they vomit in an alley just isn't Christmas."
According to the Associated Press, bar owners in New York City bar owners have barred Santas from their establishments, posting "Santacon-free zone" signs and drafting security to help them manage rowdy Father Christmases. "Take your body fluids and public intoxication elsewhere", one sign read. Diem Boyd is a member of a protest group who made and distributed the signs to unhappy bar owners. He told AP: "Now we have a whole day of vomiting and vandalism and people acting without any decorum or respect for other people. I think anything quaint about it is gone by now."