He didn't have his coffee in the morning, so he was grouchy all day.

grouchy 是形容词，来自名词 grouch（爱发牢骚的人），加上形容词后缀 -y 表示"具有...特性的"。grouchy 形容人"脾气暴躁的、爱发牢骚的"，通常用来描述因小事而容易生气或抱怨的状态。