I too, remember basic marketing and I agree with
almost everything you say. You wrote:

"...i wouldnt want my kids seeing the billboards. Its adult in theme, and shouldnt be viewed by those with tender eyes and innocent minds."

If the ad were printed in a magazine, there would be no problem. What makes it inappropriate is that Hard Rock placed the ad on a billboard where it can be seen by all, including young children.

On that basis, Hard Rock stepped way over the line. Just my opinion.