Green’s Dictionary of Slang

daffy adj.

also daffey
[SE daft]

[late 19C+] eccentric, foolish; esp. in daffy about, daffy on, madly in love with.

In compounds

daffy chariot (n.)

[1910s] (US) an ambulance for conveying the insane to hospital.

daffy-headed (adj.)

[1980s+] foolish.

daffy house (n.) (also daffy joint) [joint n. (3b)]

[1900s] (US) a psychiatric institution.