>Show no surprise or concern.
>To not react to something.
>To show no sign of surprise or worry when something unexpected happens:
>To not display even a hint of an emotional response, such as consternation, annoyance, sadness, joy, etc.
Example
>How can you just sit there calmly and not bat an eye when your boss yells like that?
>She told him she’d spent all her savings but he didn’t bat an eyelid
>I probably sound like a broken record, but I don’t want you to forget.