The kiwi is the national bird of New Zealand. The fruit is named after it (much later). Typical NZ slang has NZers referring to themselves as Kiwis. Our dear dear cousins across the ditch (aussies in case that not immediately obvious) call us that, where as we call the Aussies ( or bogans). Yanks is abbreviation of Yankees, a affectionate nickname taken from WWI (I believe) when US soldiers served alongside the Brits and her colonial lackeys... I mean subjects. All slang is pretty much affectionate, not meant to be a diminutive or derogatory... mostly.. ;-)