audacious意思是“敢于冒险的，大胆的”，audacious in the extreme的意思是“胆大包天”。

【例句】
Now that they were backed up, these fellows became audacious in the extreme.
一旦有人撑腰，这帮家伙就变得胆大包天。

You are extremely audacious in the extreme to steal a purse in broad daylight!
光天化日下抢钱包，你真是胆大包天。