Could have several meanings, depending on the way it's said. Just to give you an impression here are two short conversations: A: Maybe you left your wallet on the table? B: That's it! Of course! I went to the bathroom and left it on the table. A: I think the Yankees are the worst squad in the league. B: That's it! I've had enough of your crap! First one is positive and the second one is negative. Good luck!

有很多意思 1）就这么多了。当你点餐的时候，点了很多，最后说that's it就是表示结束就这么多了 2）你看看吧。有些责怪 3）打住（别说了） 还有很多种，我暂时就想这么多

那是它?