WordNet sense 1 (characterized by a lightly pert and exuberant quality):

impertinent, irreverent

WordNet sense 2 (displaying animation, vigor, or liveliness):

spirited

WordNet sense 3 (improperly forward or bold):

fresh, impudent, overbold, sassy, smart, wise

WordNet sense 4 (used of temperament or behavior; lacking restraint or modesty):

forward