BE nice to that police officer strolling around your neighbourhood or putting a ticket in your car. Chances are, underneath that green uniform, breathes an aspiring Ken Hom. Unbeknown to many, the Royal Hong Kong Police Force maintains an auxiliary staff of police who are well-trained in cooking and catering. The volunteers attend an eight-week course in basic Cantonese cooking. After their final examination, they return to normal duty. In the case of emergency, they can be summoned to change their uniform and man the woks. ''Some people underestimate the importance of feeding the police well. They need three good meals a day, or more,'' explained John Parker, force catering officer, of the Royal Hong Kong Police Force. Parker oversees the graduation of six classes annually. A final examination was held recently at the Tai Po Catering School in the New Territories. Judging from the looks and taste, five officers who shook woks, chopped garlic and skilfully garnished plates of fried shrimp and chicken with cashews, showed nosigns of nervousness. Each had to execute three dishes - compoy soup, batter-fried shrimp and chicken with cashews. The students were evaluated on ingredient preparation, skill and technique, presentation and taste. Of the five, highest marks went to the two women. ''They toss those [woks] around like pillows,'' remarked one judge. Judges included Chris Baker from The Wine School, Diane Boulton of Pacific Wine Cellars and Bronwyn Kerr of Seagram Hong Kong. CONSUMERS, beware. Before you order a martini in the Noon Gun Bar of the Excelsior, name your size. The martinis served there are usually well-made and, by Hong Kong standards, average in generosity. If you toss in the spectacular view of the harbour at dusk, the warm nibbles, and the tranquility of the lounge, the cocktail merits the $39 price tag. But one customer recently reported a sobering experience. She ordered an Absolut martini and enjoyed it immensely. Then she ordered a second. When the bill arrived, it felt like a bucket of iced-water. ''Why is this so expensive?'' she enquired of David, the bartender. The price was just short of $180. ''It's our jumbo,'' he responded, pointing to its entry on the drink menu. ''We always serve a jumbo unless the customer asks for a single.'' When the Excelsior was informed, Patsy Chan was apologetic. ''It was a slip up by the bartender,'' explained Ms Chan. ''They are supposed to ask the customer first what size they want.''