[DanBC]

Neal Stephenson writes about this in one of his books -- not sure which. A character wonders why "Brit" or "Ausie" are acceptable, while "Jap" or "Paki" are not.

He doesn't mention the use of the word Paki by neo-nazi far-right racists.

Edit: in the UK it's almost always a slur. I can see how in other places it's just an abbreviation.