"laugh up your sleeve" in Chinese (Simplified)
Definition
对某事偷偷感到好笑，尤其是在别人不知道或者不会同意时。通常指对别人的失误或不幸暗自得意。
Usage Notes (Chinese (Simplified))
这个短语带有委婉、隐晦的意味，通常在书面语比口语中常见。强调暗自开心或幸灾乐祸。常和“偷偷地”、“暗地里”搭配。很少用于字面意思。
Examples
She couldn't help but laugh up her sleeve when her brother tripped over his shoelaces.
她忍不住**暗自发笑**，当她哥哥被鞋带绊倒时。
He laughed up his sleeve at his competitor's mistake during the game.
他在比赛中对手的失误**偷偷笑了**。
The teacher noticed some students laughing up their sleeves during the class.
老师发现有些学生在课堂上**偷偷笑**。
Everyone pretended to agree, but you could tell they were all laughing up their sleeves.
大家都假装同意，其实都在**暗自发笑**。
He acted serious about the plan, but I knew he was laughing up his sleeve at the idea.
他对计划装得很认真，但我知道他其实在**暗自发笑**这个想法。
When his rival forgot her speech, he just smiled politely but was definitely laughing up his sleeve.
当他的对手忘记演讲时，他只是礼貌地微笑，其实在**暗自偷笑**。