not say boo to a goose
US /nɑt seɪ buː tu ə ɡuːs/
UK /nɑt seɪ buː tu ə ɡuːs/

1.
大声说话都不敢, 非常胆小
to be very shy and quiet, and unable to speak to people you do not know
:
•
She's so timid, she wouldn't say boo to a goose.
她太胆小了,连大声说话都不敢。
•
Despite his tough appearance, he wouldn't say boo to a goose in real life.
尽管他看起来很强硬,但在现实生活中他连大声说话都不敢。