As tough as nails.

　　Reckon without one's host.

　　To be a law unto oneself.

　　eg：Our boss is stubborn as a mule, never takes any one's advice.

　　中英俚语俗语来源：苏东坡后集·谢宣召入学士院状：“知臣刚愎自用，虽有宽饶(盖宽饶)之狂，察臣招摩不移，庶几长市之守。”

　　反义词：不耻下问 Bow down thy ear.