Source : Webster's Revised Unabridged Dictionary (1913)

Self-assertion \Self`-as*ser"tion\, n.
   The act of asserting one's self, or one's own rights or
   claims; the quality of being self-asserting.

Source : WordNet®

self-assertion
     n 1: the act of putting forth your own opinions in a boastful or
          inconsiderate manner that implies you feel superior to
          others
     2: the act of asserting yourself in an aggressive manner