During the Tang dynasty, there was a treacherous court official named Li Lin Fu. He was known for his flattery of the Emperor and skill in the political scene, which enabled him to remain powerful throughout his lengthy duration as the prime minister.
To secure his power, he cut off all routes for all potential political challengers, including false accusations against other officials and the granting of key military commands to non-Han commanders. He did all these underneath a mask of friendliness.
The Emperor then asked Li Lin Fu for his opinion, Li Lin-fu acted very indifferently, saying "I knew about the gold mine a long time ago, and I didn't tell it to your Majesty on purpose."
"Why?" said the king in surprise.
"According to Taoist principles, Hua Mountain is in the place where all of Your Majesty's auspicious aurora are gathered. Any damage to that area will certainly be harmful to your health and state. Who is it that brings out such a foolish idea? "
Hearing this, the Emperor thought that Li Shi Zhi was not as considerate as Li Lin Fu, and later demoted the former to remote area.
Background and Writer Comment:
Now the idiom of Honey-Mouthed And Dagger-Hearted--Kou Mi Fu Jian is often refer to those with an honey tongue and a heart of gall.
This idiom has quite a few English counterpart, such as "a fox in a lamb's skin", "treachery lying underneath a mask of friendliness" and "Bees that have honey in their mouths have stings in their tails"