not say boo to a fly(redirected from couldn't say boo to a fly)
not say boo to a fly
To be particularly shy, diffident, or timid by nature. Primarily heard in Australia. My brother is a very sweet, warm-hearted man who wouldn't say boo to a fly. How can you suspect him of committing this crime? The neighbour's daughter is just the cutest little thing, but she couldn't say boo to a fly.
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