he, she, etc. wouldn't harm/hurt a fly

wouldn't harm a fly

Is particularly shy, diffident, or timid by nature. My brother is a very sweet, warm-hearted man who wouldn't harm a fly. How can you suspect him of committing this crime?
See also: fly, harm
Farlex Dictionary of Idioms.

wouldn't hurt a fly

or

wouldn't harm a fly

If someone wouldn't hurt a fly or wouldn't harm a fly, they are very kind and gentle. She was such a lovely girl, who wouldn't have hurt a fly. He is, he insists, a pacifist, who would not harm a fly.
See also: fly, hurt
Collins COBUILD Idioms Dictionary, 3rd ed.

wouldn't hurt (or harm) a fly

used to emphasize how inoffensive and harmless a person or animal is.
See also: fly, hurt
Farlex Partner Idioms Dictionary

he, she, etc. wouldn’t harm/hurt a ˈfly

he, she, etc. is kind and gentle, and would not hurt anyone: The dog may look very fierce, but he wouldn’t hurt a fly.
See also: fly, harm, hurt
Farlex Partner Idioms Dictionary
See also:
  • wouldn't harm a fly
  • not say boo (to anyone)
  • not say boo to a fly
  • not say boo to a goose
  • wouldn't hurt a fly
  • not hurt a flea
  • not hurt a fly
  • can't say boo to a goose
  • he, she, etc. wouldn't say boo to a goose
  • wouldn't say boo to a goose