Interesting thread in a thread.
The last time I used the word was at Dunsfold in 1984 when I was briefing 4 chaps before demonstrating some flight test techniques to them in a Seminole. I was talking about spiral stability and said "the nigger in the woodpile is control circuit friction". The three white youths looked horrified and the black lad just grinned. I guess he realsed there was no racist intent on my part and that the common colloquial expression (at least when I was a lad) was just that.
In my view many adherents of PC fail to take the circumstances into account and as a result bring genuine PC (which I fully support) into disrepute. Shame really.