A terrific comedy about young Los Angeles dudes on the prowl. The characters drink martinis and dress in silvery-suave style, but they also talk with a nervous, imploring incessantness, microanalyzing the rules and rituals of love in the '90s. Director Doug Liman captures something hilarious and touching — a new attitude of wistful modesty on the part of young macho cruisers. As Trent, a handsome shark who tells Mike (Jon Favreau), the self-pitying hero, ''You're money!'' Vince Vaughn is spooky-cool sexy, like the young Christopher Walken. A