not 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
Farlex Dictionary of Idioms.
See also:
  • not say boo (to anyone)
  • not say boo to a goose
  • he, she, etc. wouldn't say boo to a goose
  • wouldn't say boo to a goose
  • he, she, etc. wouldn't harm/hurt a fly
  • wouldn't harm a fly
  • can't say boo to a goose
  • not hurt a flea
  • not hurt a fly
  • wouldn't hurt a fly