too much knowledge of something, or the fact that you know it too well

It would be easy, through over-familiarity with the facts of climate change, to fail to appreciate the true implications for our future. 由于过于熟悉气候变化的实际情况，很容易无法领悟气候对我们未来的真正影响。

The lesson topic was not uninspiring. The problem was simply laziness and over-familiarity on the part of the teacher.

behaviour that is too friendly and informal

The word "mate" has an uncomfortable over-familiarity to it when used between men who have never met before.

Her tone was firm and she spoke with warmth, but no overfamiliarity. 她语气坚定，措辞热情，却又不至于过分亲昵。