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.
See also: boo, fly, not, say