not hurt a fly

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]

Words nearby not hurt a fly

not have anything on, not have it, not have one's heart in it, not have the heart to, not having any, not hurt a fly, not if one can help it, not if you paid me, not in the least, not know beans, not know enough to come in out of the rain