[throw_away]

The only people I've ever encountered using the "a (Japan|Chin)ese" construction were (Japan|Chin)ese people themselves. Which may have rubbed off on GGP from GGP's Asian spouse. I've wondered if there was some correlation in Asian languages, but the English translation of the Japanese version of that wiki page makes it seem as if the concept of demonym is foreign to Japanese readers: http://translate.google.com/translate?hl=en&sl=auto&tl=en&pr... (and there's no Chinese version, as far as I can tell).

[bluedino]

It's also a way older people or rural/Southern people would refer to African-Americans: "She dates a black"

Most people would think that's an odd or deragotory way of saying that.

[philwelch]

They're probably doing a s/negro/black in their head.