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

“He’s spent 46 years in prison … and has not hurt a fly,” said Woods’ attorney, Dominique Banos, CNN reported.

From Washington Times

Neighbors who live in the retirement community where the discovery was made said that Sourone-Mathers was a "very nice person" who would not "hurt a fly."

From Fox News

Ciccolo’s mother has said her son “would not hurt a fly.”

From Seattle Times

"He would not hurt a fly," Imam Akonjee's nephew Rahi Majid, told the newspaper.

From BBC

He had told investigators he "would not hurt a fly" after his capture in April.

From BBC