He was daffy about her and she could twist him around her little finger. 1922, F. Scott Fitzgerald, chapter IV, in O Russet Witch!:
"You've gone so plum daffy you are forgetting your dinner," jeered her mother. 1909, Gene Stratton-Porter, chapter I, in A Girl of the Limberlost:
Now I'm hungry as a Rocky Mountain lion so come, let's go and get this poor, daffy, tealess widow and wine and dine with her and make it all up. 1898 September 30, Willa Cather, The Westbound Train:
An allusion to an old medicine known as Daffy's Elixir.
Meanings
(UK, dated, slang, uncountable) Gin.
1837-39, Charles Dickens, Oliver Twist
“Do you give the children Daffy, Mrs. Mann?” inquired Bumble, following with his eyes the interesting process of mixing.
[…] he failed repeatedly until he took over his famous house in Haymarket, where for many years, surrounded by such admirers as Byron, Tom Moore and Hazlitt, he smoked his yard of clay, drained his glass of 'daffy', and […] 1954, Denzil Batchelor, Big Fight: The Story of World Championship Boxing, page 44:
Within Castle Tavern, at Holborn, Charles Perth and Lord Lucan were drowning their disparate sorrows in a glass of daffy. 1991, Julie Caille, Change of Heart, page 255: