Years back, there was a popular but extremely racist expression (I used to see it in Agatha Christie’s novels) that people used when they sensed that something suspicious was happening: “There’s a nigger in the woodpile.”
In different movies, W.C. Fields would “clean up” this expression by saying, “I sense a Dubangi in the fuel supply” or something along those lines.
Well, it was W.C. Fields: she probably preferred younger and sexier than him. (She was 13 years younger than him, and pretty enough to be choosy about who she locked inside her bedroom).
Many years ago a much older co-worker used the expression “There’s an Ethiopian in the Lumber Yard,” which took me a second to translate. I recognizede the Fields quote as the same class of genteel-ly re-worded expression as soon as I read the OP. I suspect that the OP’s inability to do the same is mainly due to the original phrase’s falling out of favor, being greatly un-PC.
Yay!
Nigger in the woodpile or Nigger in the fence starts appearing in print around the 1840’s. It probably was a not uncommon expression even before that time. It meant, to most at that time, something that was out of place, unexpected, a trick, something to be considered a drawback.
The use of the phrase to indicate a potential black forebearer of a white person doesn’t appear until the mid 1900’s.