The Collaborative International Dictionary of English v.0.48:

Pertness \Pert"ness\, n.
   The quality or state of being pert.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pertness
    n 1: inappropriate playfulness [syn: impertinence,
         perkiness, pertness, sauciness, archness]
    2: quality of being lively and confident; "there was a pertness
       about her that attracted him"

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "pertness":
   activity, aggressive self-confidence, airiness, animation, ardor,
   arrogance, audacity, bold front, boldness, bounce, brash bearing,
   brashness, brassiness, bravado, brazenness, breeziness, brio,
   briskness, bumptiousness, buoyancy, carefreeness, cheekiness,
   chestiness, chirpiness, cockiness, conceit, conceitedness,
   contempt, contemptuousness, daring, daringness, debonairness,
   defial, defiance, defying, derision, despite, disdain, disregard,
   elan, enthusiasm, glow, gusto, immodesty, impertinence,
   impetuosity, impetus, impudence, insolence, jauntiness,
   joie de vivre, levity, life, light heart, lightheartedness,
   lightness, lightsomeness, liveliness, lustiness, mettle,
   obtrusiveness, perkiness, resilience, robustness, sauciness,
   self-assertiveness, self-conceit, side, spirit, spiritedness,
   swelled head, swelled-headedness, vivacity, warmth, zest,
   zestfulness