Once a year, on the third Sunday of December, it is not merely permitted but correct to hurl insults at a religious procession in Japan. The place is Iizuna Shrine, tucked behind Mount Atago in Kasama, Ibaraki — tengu country, by local legend — and the event is the Akutai Matsuri, the Festival of Abuse, counted with the cheerful looseness of such lists among Japan's three great bizarre festivals.

Thirteen parishioners dressed in white, standing in for tengu goblins, climb in silence from altar to altar, leaving offerings at small shrines along the mountain path. The crowd follows, shouting: Bakayaro! Hurry up! The louder the abuse, the cleaner the year ahead — and whoever wrests away an offering claims health and household peace for the coming year. The custom is said to date to the mid-Edo period, when the local lord devised it as a way of hearing, once a year and at top volume, what his people really thought.

There are rules, as there always are in Japan. No personal attacks; the tengu carry green bamboo staves and will use them, gently, on anyone who crosses the line. Even abuse, here, has manners. The shrine sits in the Iwama district of Kasama, about ten minutes by taxi from Iwama Station on the Joban Line, an easy day trip from Tokyo, with Kasama's pottery town nearby. Bring a loud voice and a year's worth of grievances.