Brandon Singleton was 8 when he first saw the movie "Clueless," and it changed his life. He was entranced by the paradise of teenage consumption that the 1995 film portrayed, a Hollywood world of valet parking and designer duds. So when he entered Suitland High School in Prince George's County four years ago, he was determined to make it his reality. Now 17, he wears Armani sunglasses inside his mother's modest townhome on a recent afternoon as he rattles off a list of his favorite designer brands: Dolce & Gabbana, Coach and "a little Burberry here and there." His first...