BEST KNOWN for a music video of her playing the violin in a wet T-shirt, half-Thai, half-Chinese Vanessa-Mae Vanakorn Nicholson can hardly be accused of being conventional. Even so, the way she spent her 18th birthday on Oct. 27 was decidedly different: on stage at the Hong Kong Coliseum before some 7,400 people. Playing her signature white electric Zeta (pictured), as well as a 200-year-old classic she owns, the Singa-pore-born, London-based pop-violin diva performed eight numbers. One of them, a Scottish ditty called I'm a Doun for Lack o'Johnnie, has been released as a CD single, her first recording as a singer. The audience did some crooning too: they sang Happy Birthday, visibly moving Nicholson. Sounds like a concert she and her Hong Kong fans will not easily forget.