Soon M.B.A. students at UC Davis will take the single most important one-day course in their professional school training -- an etiquette course, designed to help business graduates improve their manners for job interviews. With an 80 percent chance that an interview will include one or more meals, etiquette is important, according to instructor Shirley Willey of Etiquette and Company in Sacramento. Fifty students from the UC Davis Graduate School of Management will learn table manners, place settings and the proper method for holding a fish knife, during their three-hour course on Friday, Feb. 25, at the University Club on campus. Willey says that while perfect manners alone won't snag a job, a shoddy showing may be just enough to cost graduates that dream position. She tells of an impeccably dressed graduate student with a 3.8 grade point average who lost a job after he used his thumb to push rice onto his fork. This year's course will include international etiquette tips.