poker-faced 扑克脸，面无表情的

Poker-faced – expressionless (comes from the game of poker where you must not let your face reveal whether you have a good or bad card)

扑克脸 - 面无表情的（来源于扑克游戏，玩扑克时不能让表情泄露自己是牌好还是牌坏）

例句：

The clients sat poker-faced all through my sales pitch. It was so unnerving. (Poker)

在我整个宣传推销过程中客户始终面无表情地静坐，这让人感到很气馁。（扑克游戏）