laugh up one's sleeve
形容某人表面同情實則暗喜
例句
While pretending to sympathize, she was laughing up her sleeve at his misfortune.
典故來源
源自16世紀，當時人們用長袖遮住嘴巴偷笑，避免被察覺，后引申為暗中幸災樂禍。