keep a straight face

US /kiːp ə streɪt feɪs/
UK /kiːp ə streɪt feɪs/
"keep a straight face" picture
1.

保持严肃, 不笑

to succeed in not laughing or smiling

:
It was hard to keep a straight face when he told that ridiculous joke.
当他讲那个荒谬的笑话时,很难保持严肃
She tried to keep a straight face, but a giggle escaped.
她努力保持严肃,但还是忍不住笑出声来。