As John Lawler has explained, "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."
Whether "don't you do that" sounds more or less bossy, largely depends on the intonation one uses. It can be a friendly and loving "don't you do that...no....please...not here" or a real order "DON'T YOU DO THAT !!!"