“you” 要的。這是一種強調的語氣 ：）

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."

Click this link to see more：

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