Silly, goofy, or scatterbrained in a humorous way; not serious or sensible.
Possibly derived from 'daft' through dialectal variation, or from British slang. Popularized in the mid-20th century, especially through cartoon characters like Daffy Duck.
Daffy Duck's unpredictable, chaotic behavior perfectly captured the meaning—while 'daft' sounds mean-spirited, 'daffy' feels affectionate and fun, which is why the duck could get away with destroying his own cartoons!
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