puerile
🇺🇸
/ˈpjʊrəl/
🇬🇧
/ˈpjʊəraɪl/
acting like a child in a way that is not suitable for an adult
His puerile behavior at the formal dinner was embarrassing to watch.
他在正式晚宴上的幼稚行为令人尴尬。