Como dizer "Que Coisa!" em inglês

Suggestion:

I've told you not to do that! Good grief!

How many times do I have to repeat myself (before you do what I say)?

Source: from somewhere in the Web. WordReference, perhaps.

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How many times do I have to tell you?
1. Not to talk with your mouth full, 2. Not to talk when your mouth is full, 3.not to talk when you're eating)?

Source: ditto.

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How Many Times Do I Have To Say The Same Thing ("over and over/over and over again" - just for emphasis) ?

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Other "tool" for emphasis is to use "What´s the matter with you?" in the beggining of the sentence, or in then end.

How many times do I have to tell you not to talk with your mouth full? What´s the matter with you?

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Let´s wait for more.

Que coisa! Honestly!

Honestly: informal — used to express annoyance or disapproval. (merriam-webster)

Leave me alone! Honestly!
Me deixa em paz! Que coisa!

Eu já falei pra você não fazer isso. Que coisa!
I've told you not to do that. Honestly!

Bons estudos.

Other ways to express that exasperated grrrr-moment is "damn!" or "what the hell/sh*t! ", it would work to both situations. But it can be sometimes an impolite thing to say.

Contribuição

Gosh! = que coisa!

Fonte: Dicionário Português/Inglês - Porto Editora