If you haven’t heard of Santacon before, this year’s holiday season is as good a time as any to hear of it. Santacon is, in a nutshell, this: It’s a mass gathering of people who come together in cities across the world, all dressed in Santa costumes. They parade on streets and drink in bars and have a jolly good time spreading cheer and singing naughty Christmas carols. Widely known as Naughty Santas or Santarchy, this festive movement has been growing each year. Beginning first in San Francisco in 1994, the event is a bit of a flash mob that tends to shock whoever is around. The gathering manifests itself differently in each city ever year, but for a peak into the kind of activity you can expect in, say, New York City subways, watch this video and then check out this list of Santacon events so you can participate or just watch in the town nearest you.