Utter shamelessness; brazen and unscrupulous behavior with no sense of embarrassment — a four-character idiom used to strongly criticize someone.
彼は借金を踏み倒して平然としている、まったく厚顔無恥だ。
He defaulted on his debts and acts as if nothing happened — utterly shameless.
そんな要求を続けるなんて、厚顔無恥と言わざるを得ない。
To keep making such demands, one can only call it shameless.