not hurt a fly

Idioms  

1. Also, not hurt a flea. Not cause harm to anyone, be gentle and mild, as in Paul's the kindest man—he wouldn't hurt a flea, or Bert has a temper but it's all talk; he wouldn't hurt a fly. Both fly and flea are used in the sense of “a small insignificant animal.” [Early 1800s]

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Example Sentences

These gestures of gallantry, this attunement to the sweet and fatal charms of women, this radical compassion, are Tristram’s inheritance from his uncle, the man who would not hurt a fly:

From Slate • Feb. 8, 2016

Absolutely, take away dangerous items and instead populate the floor with soft, squishy balls that could not hurt a fly.

From Washington Post • Dec. 9, 2014

It is a face of child-like innocence, a young woman who would not hurt a fly.

From BBC • May 6, 2013

It was said that these lost girls were sweet as honey and would not hurt a fly.

From "Between the World and Me" by Ta-Nehisi Coates

Soren was a kindly and genial soul, who would not hurt a fly as long as he was left to sail his Birkebeineren in peace.

From Dry Fish and Wet Tales from a Norwegian Seaport by Nilsen, Anthon Bernhard Elias