Why can't you just say what you mean?

Recently my Japanese conversation partner and I were talking about Japanese culture as reflected in the language itself. In the story I'm currently translating, I had come across anmoku no ryokai (暗黙の了解) which means "a tacit or a silent understanding." 

That led her to teach me the word inginburei (慇懃無礼) which according to my electronic dictionary means:

—insolent under one's civility

—rude under a veneer/mask of politeness

—rude under the surface

—politely insolent

—rude while preserving the outward forms

—studied insolence.

In other words, someone may appear polite, but beneath they are seething. That's when you'll need some tacit understanding.