Not bat an eyelid
Definition 1 of 1
Pro Tip 1/3Emotional Control
The phrase often describes someone remaining calm and composed when a reaction is expected. 
When she heard she'd won the lottery, she didn't bat an eyelid.
Pro Tip 2/3British Origin
This phrase is commonly used in British English, demonstrating their cultural stereotype of stoicism. 
After scoring the winning goal, he didn't bat an eyelid, as if it was nothing special.
Pro Tip 3/3Informal Expression
Used mainly in informal conversation and writing, not in formal or official communication. 
She spilled her coffee all over the table but didn't bat an eyelid.