From Longman Dictionary of Contemporary Englishdaffydaf‧fy /ˈdæfi/ adjective informal silly or crazy in an amusing way
Examples from the Corpus
daffy• Sabina is beautiful but a little daffy.• Like an amiable but daffy uncle, he repeatedly hangs himself with his own anecdotes.Origin daffy (1800-1900) daff “stupid person” ((14-19 centuries)) 