A quick word on racial abuse. Questioning the rationale behind something being found offensive very rarely comes across intelligently. I would surmise that although both are simply shortenings of a full and frank description, terms such as 'Jap' and 'Paki' are widely found to be offensive due to persistent pejorative use over time. My brother and I have held lengthy shitstorm arguments over this, owing to the fact that he has several Pakistani friends between whom the word 'Paki' is tossed around with affection. The thing is, where you cannot rely on the same affectionate bond, use of the term will bring your thinking on such issues to the top of the agenda. They're only words, and you have a right to use them. But if you do not show respect, then you are likely to get called on it.
I have by no means said everything that bears saying on this subject, but I hope I have cast a net wide enough to wrap this issue up until someone actually starts a thread on it, and to allow the purpose of the original discussion to run its course?