The phrase "defiant act" refers to an action or behavior that shows resistance or disobedience towards someone or something of authority. It is an act done with a strong determination to challenge rules or norms. Full definition
The Orphan Master's Son is a richly textured political thriller about the hidden world of North Korea with all of its misery, violence and defiant acts of love under impossible circumstances. (amazon.com)
His first defiant act was to not play basketball and take advantage of his height, but to apprentice himself in his mother's beauty shop. (hammer.ucla.edu)
Patience for the 3:00 a.m. feedings; patience for teething; patience for toilet training; patience for the dreaded «terrible twos»; patience for your child's first outright defiant act. (fathers.com)