IF IT'S good enough for New York City, it's got to be a starter in this similarly paranoid metropolis. We're talking slogans here, of the kind David Letterman invented last week to present to Rudolph Giuliani, the feisty mayor of NYC. The slogans (among them 'Home of the US$6 Cup of Coffee' and 'The Bus Fumes are Free', with the winner being 'We Can Kick Your City's Ass') were obviously aimed at giving the Big Apple an edge in the image department. And, let's face it, we could all do with that. So how about a few of the following appearing on Tourist Association brochures or perhaps as Porsche bumper stickers: 'Come rattle our cages!' 'One country two cisterns' 'Hong Kong: where children are obscene and not heard'. 'Just say 'Chek Lap Kok' and you're there!'