You Know What They Say... “I Don’t Know You From a Bar of Soap.”
The earliest quotation is from the following cartoon by Stan Cross (Stanley George Cross – 1888-1977), published in Smith’s Weekly (Sydney, New South Wales) of Saturday 26th November 1938—this cartoon depicts two down-and-out men in a public park; one, sitting on a bench, says to the other, standing beside him, with a bundle under his arm:
I don’t know you from a bar of soap
The other replies:
No – I suppose we’re both strangers to you
The caption is:
SAYS HE SCORNFULLY: “I don’t know you from a bar of soap!”
However, the earliest uses of not to know — from a bar of soap that I have found date from the late 19th century, and are from U.S. publications—except two, which are from Australian newspapers.
The earliest occurrence punningly contrasts two acceptations of the noun bar; it is from The Chicago Daily Tribune (Chicago, Illinois) of Wednesday 30th May 1877—itself quoting the St. Louis Globe-Democrat1 about “the Soldene2 troup”:
“The ‘prima donna’ does not know a bar of music from a bar of soap; the chief actor would not be allowed to play supernumerary in a dumb show […].”
1 I have searched in vain for the original article in the St. Louis Globe-Democrat (St. Louis, Missouri).
2 Emily Soldene (1838-1912) was an English comic-opera singer, actress-manageress, novelist and journalist.
The very same punning use of bar occurs in the St. Louis Post-Dispatch (St. Louis, Missouri) of Saturday 6th January 1883, about the last-minute cancellation of a concert by the Swedish opera singer Christina Nilsson (1843-1921):
The young men of fashion who—to use a vulgar expression—don’t know a symphony from a sardine, and could not tell a bar of music from a bar of soap, but who in deference to the dictates of fashion had bought tickets for to-night—they are not wholly unhappy and do not mourn as those who refuse to be comforted.
The phrase not to know, or not to be able to tell, a bar of music from a bar of soap has been regularly used since then.
- Pascal Tréguer
“Meaning and Origin of the Phrase 'Not to Know - from a Bar of Soap'.” Google, Google, www.google.com/amp/s/wordhistories.net/2019/11/13/know-bar-soap/amp/.