Meaning of the word "wouldn't hurt a fly" in English

What does "wouldn't hurt a fly" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

wouldn't hurt a fly

US /ˈwʊdnt hɜrt ə flaɪ/
UK /ˈwʊdnt hɜːt ə flaɪ/

Idiom

to be gentle and harmless; to be incapable of causing harm to anyone or anything

Example:
Despite his intimidating appearance, he wouldn't hurt a fly.
My grandmother is so sweet; she wouldn't hurt a fly.