All my google-fu hasn’t been able to produce an answer to this question.
Why do we associate ghosts with the word “boo”?
I can’t even think of a pop-culture reference to a ghost saying “boo,” yet it’s a universally recognized meme. Pictures of ghosts are almost inevitably captioned “BOO!” and anyone who dresses up for Halloween as a ghost (by wearing a sheet with holes cut out for the eyes, of course) will say “boo” to whoever they meet. Ask anyone what a ghost says, and the answer will invariably be “boo”! But has a ghost in fiction or in reported fact ever actually said “boo”? Where does the idea come from?