IPA: /ˈpɛtʃ.ə.lən.si/
KK: /ˈpɛtʃələnsɪ/
A state of being easily irritated or annoyed, often in a childish manner.
Her petulancy was evident when she didn't get her way during the meeting.
Petulancy is derived from "petulans" (from Latin, meaning to be rude or impertinent) and the suffix "-cy" (meaning the state or condition of). The word describes the state of being rude or irritable, often in a childish manner.
Think of someone being rude or irritable, which is what 'petulancy' means — it captures the state of being petulant.