【Shameless】 , 【brazen】 ,  【barefaced】 ,  【brash】 ,  【impudent】  can apply to persons and their acts that defy the moral code or social decorum when they mean characterized by boldness and a lack of a sense of shame.

【Shameless】 implies a lack of effective restraints (as modesty, a sense of decency, an active conscience, or concern for the respect of others).

【Brazen】 implies not only complete shamelessness but defiant insolence.

【Barefaced】 implies absence of all effort to disguise or to mask one’s transgressions; it connotes extreme effrontery.

【Brash】  so strongly implies impetuousness that it does not stress shamelessness as clearly as the preceding words; however, it is often used in place of  【shameless】 when heedlessness and temerity make one indifferent to the claims of conscience or one’s sense of decency.

【Impudent】  adds to  【shameless】 implications of bold or pert defiance of considerations of modesty or decency.