Not say boo to a goose
Definition 1 of 1
Pro Tip 1/3Cultural Image
This phrase uses the image of a harmless goose to emphasize someone's timidity. 
Although he's a talented musician, he's so timid he wouldn't say boo to a goose.
Pro Tip 2/3Non-Literal
Understand that this phrase is not about geese; it's an exaggerated way to describe shyness. 
Even though the error was not her fault, she didn't say boo to a goose and accepted the blame.
Pro Tip 3/3Emotional Connotation
The phrase can imply vulnerability or a non-confrontational nature, not just shyness. 
He's the kind of person who wouldn't say boo to a goose, always avoiding conflict.