[xiào bǐ hé qīng]   

笑    比    河    清    形容态度严肃，难见笑容。

故事里由于包拯铁面无私，一年时间就把开封治得井井有条。权贵们都收敛了许多，一听到包拯的名字就怕，说要看到包公的笑脸比看到黄河水变清还难。老百姓却很喜欢他，说：“关节不到，有阎王包老。”

To make one smile is as difficult as to purify the river

笑不可支    笑容可掬    笑歌戏舞    笑傲风月    笑中有刀