An intrepid insect briefly stole the spotlight at an otherwise elegant affair to celebrate “Downton Abbey” Monday. “Oh my, there goes a cockroach!” exclaimed Hugh Bonneville, the series’ suave Earl of Grantham, when a brown critter skittered across the floor during a Q&A in front of cast members including Michelle Dockery (Lady Mary) and Elizabeth McGovern (Countess of Grantham). PBS Masterpiece head Rebecca Eaton abandoned her role as interviewer to squash the insect as the audience let out a collective, “Ewwwww!” “How can I top that?” Bonneville quipped. Jim Carter, who plays butler Mr. Carson, said of the squished creature, “That could have been Shirley MacLaine!” He further recalled in reference to the newest “Downton” star’s belief in reincarnation that he and MacLaine toured an Egyptology exhibit at the home where “Abbey” films, and when Carter remarked how interesting the relics were, MacLaine shot back, “I know, I lived there.” McGovern added of MacLaine, who plays her mother this season, “There’s an American style of acting, an English style of acting, and then there’s a Shirley style of acting.” Also at the Vanity Fair- and Ralph Lauren-hosted event were Patricia Clarkson, Tom Brokaw, Eric Schmidt, Steve Rattner, Gay Talese and PBS head Paula Kerger. Illustrating the UK import’s impressive infiltration into American culture, a reel shown before the third season premiere included references to “Downton” in New Yorker cartoons, online comedy spoofs and a Spike TV promo summarizing the series as being about “a bunch of honkeys who live in a church.”