who was the black comedian? Some of them are known for outrageous statements. Dave Chappelle? Chris Rock?

Racism isn't the same everywhere in the US. It's not even the same in one city. It's a personal thing, but like everything else it responds to social reinforcement or the lack thereof.

In that case, what makes black bigotry more acceptable in american society than white bigotry, asian, hispanic etc.

The double standard is quite real, and disturbing it is. I know directly, many years ago I experienced such racism at work.

I think, when in the context of comedy, there is more leeway. And yes black people can get away with saying more about white people but it's only because of the centuries of oppression that they have endured.