Describes a person or action that is extremely bold and unafraid, often with a nuance of recklessness or defiance. Common as a yojijukugo in both literary and everyday contexts.
彼の大胆不敵な行動に皆が驚いた。
Everyone was surprised by his daring behavior.
大胆不敵にも彼は社長に直接反論した。
Audaciously, he directly argued back to the president.