On Wednesday night in Brooklyn, in an elevator that was once used to move cars between floors of a belt factory, Oliver Jeffers destroyed months of work in front of a dozen witnesses, and then offered them a drink. The Northern Irish, Brooklyn-based artist (he’s exhibited at the National Portrait Gallery, but is perhaps best known for his children’s books and work with U2), had spent months creating a portrait of a middle-aged African American woman grasping a chicken in one hand and a viper in the other. Last night, he dipped it in a vat of green paint, a bright shade of sickly lime enamel, covering all but the top of her head. With that, an assistant passed around shots of whiskey and glasses were raised: “What’s done is done, and what’s to come is to come...”