There is some debate and I cannot say with certainty where the term originated, but what has been shown is that it definitely goes back to the early-to-mid 1970's when both Japanese cars and motorcycles started being imported in some volume.
It has definitely taken on a few forms since then, like a lot of slang does. For some, it seems to be a deriding term for Japanese cars or motorcycles, while others use it with a definite ethnic connotation.