Bié zài tā xīnqíng bù hǎo de shíhòu huìbào, xiǎoxīn tā xiàfēngbáo.
Don't report to him when he's in a bad mood — watch out, he'll let you have it.
Tips
memory
Image: a sudden storm dumping wind and hail on everything below. Used for someone in power letting their temper or authority crash down on subordinates.