Interesting about naïf/naïve; I’d call a man ‘naïve’ without hesitation.
Here in Leftpondia women (not men) will sometimes admit to having had a ‘blonde moment’, roughly equivalent to a ‘senior moment’.
Coincidental that lionello and aldi mentioned The Daughter of Time (first published 1951), because in it Josephine Tey has her protagonist reflect on Lady Elizabeth Woodville, Edward IV’s queen, thus:
She had been shut away from the world; that indestructibly virtuous beauty with the gilt hair.
Why ‘gilt’, he wondered for the first time. Silver-gilt probably; she had been radiantly fair. A pity that the word ‘blonde’ had degenerated to the point where it had almost a secondary meaning.
I’ve alway assumed that Tey meant by this that blonde tended to imply ‘dyed’, rather than ‘dumb’.
‘Blonde’ has so many potential implications that ‘blond’ has not. They simply are not equivalent in meaning, as ‘naive’ and ‘naif’ are, and therefore aren’t interchangeable.