you ain't seen nothing yet

Someone has only glimpsed or experienced the beginning of something that will become even more exciting, impressive, or important. (The word "ain't" is a colloquial form of "hasn't" or "haven't," which are sometimes used instead.)

只是瞥见或经历了一些事情的端倪，而这些事情后续可能会更加令人兴奋、令人印象深刻。(ain't这个词是hasn't或haven't的口语形式，经常会被用来代替它们。)

好戏还在后头呢

A: Well, the first act was simply divine.

哇，这第一幕简直太精彩了。

B: Stick around. You ain't seen nothing yet!

接着看，好戏还在后头呢 !

If you think that was muddy, you ain't seen nothing yet

如果你觉得那就够糟糕了那你就错了，这都不算什么，好戏还在后头呢 !