As in the anime show Shin Chan (aka Crayon Shin Chan). Involves pulling down your pants, revealing your bare butt and dancing.

A goth who has been part of the subculture since it originally came about, or a goth over the age of 40.

To bare your bum (or flip a moonie) to a passerby and give it a jiggle whilst you are at it

This term could be used to describe the action in which Subject A pulls down their pants to reveal a bare ass, and then does some sort of dance-motion whilst Subject B screams profusely and throws objects at Subject A's arse.