The standard expression is “buck naked,” and the contemporary “butt naked” is an error that will get you laughed at in some circles. However, it might be just as well if the new form were to triumph. Originally a “buck” was a dandy, a pretentious, overdressed show-off of a man. Condescendingly applied in the US to Native Americans and black slaves, it quickly acquired negative connotations. To the historically aware speaker, “buck naked” conjures up stereotypical images of naked “savages” or—worse—slaves laboring naked on plantations. Consider using the alternative expression “stark naked.”
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