久别情疏 Out of sight, out of mind. (Far from eye, far from heart. Long absent, soon forgotten. Seldom seen, soon forgotten.)
不告而别 French leave
不要不自量力 Don't put a quarter into a pint pot.
不要厚此薄彼 Don't make fish of one and flesh of another.
不畏艰难 Take the bull by the horns.
不战而屈人之兵 The supreme art of war is to subdue the enemy without fighting.
不入虎穴焉得虎子 How can one obtain tiger-cubs without entering the tiger's lair.
不经一事，不长一智 Experience is the mother of wisdom.
不胜其烦 a pain in the neck：Your little brother is a pain in the neck.
小Car笔记：
nasty-nice：笑里藏刀的
French leave：悄悄离去，不辞而别。这个用法来自于18世纪法国风俗，不通知主人而自己离开。