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My housekeeper drink two cup of coffee today, I ask her how can she sleep tonight. Am I right to say "You drink two cup of coffee today, you don't want to sleep tonight, don't you?" Is it too awful?
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You drank two cups of coffee today. You don't want to sleep tonight, do you?

With a tag, it's opposite of the final part of the statement. You don't... do you?

Just as a side note, a lot of people drink a lot more than that during the day. I'd be surprised to see someone drinking more than one cup of caffienated coffee after dinner and not having at least a little trouble sleeping, but I can have two or three throughout the working day and not have it affect me at all.
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"You drank two cups of coffee today; you don't want to sleep tonight, do you?"

Personally, I'd say: "How are you going to sleep tonight after drinking two cups of coffee?"
 BarbaraPA's reply was promoted to an answer.