What is the meaning of knock you over with a feather?

If Someone says, you look like i could knock you over with a feather, it depends on the person saying it as to the meaning: If your grandma, mum, grandad,dad,uncle,auntie says it, they mean you look like your in a daydream, or are sleepy. If a bully, or a bigger than you person says, I could knock you over with a feather, they mean you look weak and easy to hurt. Wishing you well, your answerer, Pretty-Zebra