I think people are giving Bieber way too much grief over this. He had just learned that Anne Frank was really into the pop culture of her time, so at least his comment was in context. If he didn't have respect for Anne Frank he wouldn't have taken the time to go to the museum in the first place.
I just think the kid is horrible at expressing himself and it's gotten himself in trouble before too, but people are tearing him to shreds

ruthless.