What is the meaning of 真是的
It's an interjection, which means its translation relies very much on the context it's in.

In general, it's an exclamation of disbelief or disagreement on what follows the phrase.

Examples:

你真是的， 怎么没穿鞋就跑出来了？ (Come on! You ran out without any shoes on?)

你也真是的，　这么早就把我吵醒了.　(Seriously? Waking me up this early?)

真是的,　他到现在还没来.　(He's not here yet. Hopeless!)