In the last big number of “Once More, With Feeling,” Buffy The Vampire‘s spectacular season six musical episode, Sarah Michelle Gellar’s Buffy looks directly into the camera and sings, “We’ll sing a happy song / And you can sing along.”

It’s as if writer/director Joss Whedon knew how popular the endlessly clever, surprisingly catchy episode would be with diehard fans, who memorize even spoken lines of dialog. One such fan, Clinton McClung, couldn’t stop singing it and figured there were others like him. And he’s taking the musical to theaters across the country, where Buffy obsessives are lining up to sing their hearts out with fellow fans.

The show stopped at DC’s Avalon theater last weekend, where the two showings sold out so quickly it ensured a return visit in the fall. One part Rocky Horror, one part fan convention, all parts geekfest, the show featured Buffy trivia, an awkwardly hilarious reenactment of a scene from the show and a goodie bag of props for the main event.

McClung, the tireless host, provided instructions before the show and energetically acted out key scenes, from hopping around in a bunny suit to waving around dry cleaning. And though the DC crowd was predictably restrained, they did blow bubbles, raise lighters and yell “Shut up, Dawn!” when they were supposed to. Although the aisle-dancing was disappointingly kept to a minimum, there was something beautiful about a sold-out theater full of Buffy devotees singing together—sometimes in key—in celebration of their favorite series.