What is a meaning of 真是的. I heard for many times in context something like 你真是的！ And yet I have doubts about proper meaning of this expression.
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.
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!)
As a native Chinese speaker I think it is most close to English "How can you do that?". In daily use it is often used in a critical or ironic tone after someone has done something wrong or stupid considered by the speaker. Example, after I bought a ugly shoes, my girlfriend would say:"真是的，又乱花钱".
“真是的” is just an abbreviation of “真是XX的”(you are XX indeed). But the listener might be hurt if "XX" is spoken out directly. So we say “真是的” to express what we want to say, but in a not very sharp way. The true meaning of "XX" usually can be readily inferred from the context.
For example: “你好不容易出国，居然还回来，真是的”=“你好不容易出国，居然还回来，真是傻”. The latter sentence is obviously offensive and therefore make the listener unhappy, so the speaker omits it. But the listener can easily guess what is omitted from the context.