that's done it是完成时态.has done.do it语法无误.do是及物动词.
done是动词过去分词.
其次,一些成语,俗语的意思是约定俗成的.记住就好.比如
a piece of cake
小事一桩
small potato
小人物.
供参考.
that's done it!
1.[口] 完蛋了
2.[口] 好了,行了,够了!
That's undoubtedly done it!
undoubtedly的意思是无疑地,绝对地
整句意思是
绝对完蛋啦!
完全好了!