https://www.brandeis.edu/parc/accountability/oppressivelangu...
[edit] They just removed it. Here's what they had previously: https://archive.is/NR0Zj
> The term picnic is often associated with lynchings of Black people in the United States, during which white spectators were said to have watched while eating, referring to them as picnics or other terms involving racial slurs against Black people.
The false etymology persists despite the Oxford English Dictionary definition: "A method or procedure derived entirely from practice or experience, without any basis in scientific knowledge; a roughly practical method." The OED dates the phrase's first reference to 1692.
In the Encyclopedia of Word and Phrase Origins, "rule of thumb" is additionally defined as a method by which brewers once tested the temperature of a batch of beer: They dipped a thumb in the brew.