Crazy, silly, or unconventional in a funny or entertaining way.
From British slang 'whack' (to hit), with the -y suffix creating an adjective. It evolved in the early 1900s to mean someone who acts unpredictably or comically.
A 'wacky' sense of humor is actually a sign of creativity and intelligence—studies show that people who find absurd, unexpected jokes funny tend to score higher on IQ tests!
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