No one quite knows exactly where ratchet stems from. Some say it's an evolved, colloquial form of "wretched." Others trace the etymology to Lil Boosie's "Do Tha Ratchet", which would help to explain why the justified incarceration of a shitty rapper upset so much of the south.
What is known, though, is that ratchet has come to stand for all things base and uncouth. So, it might surprise you to encounter a group of Bougie Black People in the wild or at a NSBE cookout, donned in pastel jeans, J. Crew maxi dresses, and delicate beards, taking mean mug selfies and holding impromptu twerk contests.
Do not be surprised. Bougie Black People are aware of their status as Bougie Black People. Since they're aware of their status, they're also aware of how Bougie Black People are often perceived by regular Blacks. This awareness makes them slightly self-conscious, and they deal with this self-consciousness by overcompensating their Blackness.
Often, this overcompensation results in them "pledging Delta", "starting a non-profit", "hating White people", "quoting Melissa Harris-Perry", "being Melissa Harris-Perry" or "running for President of the United States." These are not bad things. But, these are all things done while in the presence of regular Blacks.
When no regular Blacks are around, though, BBP's overcompensation results in them pretending to be ratchet. They wouldn't dare recite the lyrics to "Pop That" or put Frank's Hot Sauce on their sushi while regular Blacks are within a 50 to 100 yard radius. But, if you attended a BBP game night or coed kickball game disguised as a Bougie Black Person (Docksides, tapered jeans, and a witty t-shirt), you'd witness pseudo ratchetness.
Do not be alarmed, though. Bougie Black People's ratchetness is harmless. When pretending to make it rain, they use pretend "air dollars" instead of actual dollars. And the mean mug selfies are all in jest, as they're usually followed with friendly debates about Janelle Monae and LivingSocial.