It's a thing called "Respect". Bieber evidently does not have it nor, in all probability, will he ever understand the concept.
And I do not think the shade of Anne Frank would have been even remotely amused.
If you have never done so, go visit the sites of some of the former concentration camps. I would suggest Dachau, just outside Munich, as a starting place. Then, by all means, go to Auschwitz. Look at the pictures they have on display. Then tell me Justin Bieber was even remotely correct in what he did.
I have no respect for him as an "artist" or, at this point, as a human being. And I do not think that those of us who have seen those places I mentioned are the ones who need to "grow up".