有一种冷笑话叫老师来了
[yŏu yī zhŏng lĕng xiào huà jiào lăo shī lái le]
There exists a type of humor which might be considered 'cold jokes,' in this case when a teacher is approaching and people may jokingly refer to the moment, likely because a teacher’s presence can cause excitement or anxiety that can be parodied in jest with friends afterwards.