“you” 要的。这是一种强调的语气 ：）

I was jokingly dare him, haha 

"don't you do that" adds emphasis to "don't do that".

That's what a mother would say to a child, a teacher to a naughty pupil, a wife to a reckless husband and, as Hot Licks points out, "dare" is implied most of the time.

"William James, don't you do that! Put the cat down immediately."

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https://english.stackexchange.com/questions/210323/dont-you-do-this-vs-dont-do-this