WordNet sense 1 (marked by casual disrespect):

flip, impudent, snotty-nosed

WordNet sense 2 (exhibiting lack of respect; rude and discourteous):

disrespectful

WordNet sense 3 (unrestrained by convention or propriety):

audacious, barefaced, bodacious, brassy, brazen, brazen-faced, bald-faced

WordNet sense 4 (used of persons or their behavior; feeling no shame):

unashamed