Don't ask him about overtime, he's feeling really irritated right now.

irritated 是动词 irritate 的过去分词形式，在这里作形容词使用。irritate 由词根 irrit（刺激）和后缀 -ate（使...）组成，意思是"使恼怒、使烦躁"。irritated 表示"被激怒的、烦躁的"状态。