It's not "black" it's urban.
Black people don't have traits in their gene-pool that make them want to make baggy clothes n chains. To call it acting black is insulting to both races.
It's "urban". Simple as that. The fact Americans perceive it as 'acting black' just shows how the American media box up obvious stereotypes, very quickly and re-sell them to the public in various forms through the commercial machines and opinion-holes.
I'm from an urban city in Wales, in the UK. And we have plenty of people here in fact, many who walk around thinking they're bullet-proof. People who think... Well, are basically gangsters but still look ridiculous. It's urban mentality. It's based in evolutionary-roots. Basically the idea that you have to draw up a reputation / image of yourself that is to be feared, to not become a punching-bag.
This isn't unique to black people. It's unique to deprived envrionments full-stop. It used to be natural but it's now the monetary system which causes this. It's a circular mentality, not a healthy one. I grew out of at about 15 but am still aware of it and it's still in my roots due to the type of city I live in. It's also mentality which is born out of rebelling against what one doesn't have. Which is why you don't see affluent business men walking around dressed like 50 Cent. Well, apart from... 50 Cent.
To sum up. I know what you're saying about rich white kids but... You could say the same about rich black kids. It's just you associate this cliche' image with black people as if they own it so perceive anybody white, especially rich as stealing it. But this idea that urban mentality or these types of dress-senses or attitudes are black culture is racist nonsense.