The performer-writer Ann Liv Young belongs to the movement in the arts that was labeled Sensation in the 1990s. She performed “Snow White” naked, apart from a Disney mask on her face, while heavily pregnant. Dildos and masturbation have been part of her theatrical fare. At MoMA P.S. 1 in February she insulted a fellow artist’s work (accompanied by urination and masturbation) until management turned the lights off on her. And on Friday and Saturday she performed a one-woman “Cinderella” at the Issue Project Room in Gowanus, Brooklyn. In this, as an outspoken and trashy Southerner called Sherry, she converses with members of the audience (sometimes in a quarrelsome way) and also urinates and defecates onstage.

Having loved various comedians (notably Barry Humphries as Dame Edna) who make an art out of insulting audience members, and having seen actors urinate and defecate successfully onstage as part of larger dramas (“Macbeth,” “The Dybbuk,” “The Censor” and others), I have little squeamishness about this. But there are three things for which I was unprepared on Friday night, the New York premiere of “Cinderella”: the startling ineptitude of Ms. Young’s performance; the campy, cliquey way she assumed that everyone present already knew all about this show and her previous ones; and the silly consensus whereby most of her audience, giggling coyly now and then, encouraged her.

This reached a nadir when Ms. Young, some 85 minutes into the show, failed to defecate on cue, despite having given an advance interview advertising her ability to do so. She invited audience members to help her find ways of achieving her goal, and most obliged. They gave her cigarettes, Coca-Cola and practical advice about manipulation. They loosened her frock; she was wearing a full-length hooped dress with petticoat. They offered manual assistance. They encouraged her when she relocated to a chair after squatting over a bowl.

This went on for more than 10 minutes. Finally Ms. Young  claiming she must be nervous and admitting the show was running considerably over time  departed to complete her defecation in a restroom nearby. I was one of several (but too few) people who left at this point. I left partly because of the show’s sheer inefficiency. Principally, however, I felt that to remain would indicate that I shared the audience’s far-from-tacit consensus that Ms. Young deserved encouragement, and that this was fun or rewarding.