After missing the deadline, he was kicking himself for not starting earlier.

kicking 是动词 kick 的现在分词形式，kick 本意是"踢"。 himself 是反身代词，指代主语"他"自己。 kicking himself 是一个固定短语，字面意思是"踢自己"，引申为"懊悔、自责"的意思，用来形容对自己行为感到非常后悔的状态。