She slammed her fork on the table petulantly when the waiter took too long to serve the food.

petulantly 是形容词 petulant 的副词形式。petulant 来自拉丁语 petere（要求、寻求），形容人"易怒的、任性的"，常指因为小事就发脾气。petulantly 表示"任性地、耍脾气地"，描述一种带着不耐烦情绪的举止。