I grew up only speaking "Proper English." My mother was a teacher and nothing else was acceptable. I was still able to speak the dialect of my area (e.g., "That girl's hella dumb.") without technically stepping outside the perameters of proper grammar and syntax. It wasn't until I got to college that AAVE became a part of my language--going to a black school will do that for you.
I also picked up different dialects as I stayed in various places; it all depends on the region of the person I'm speaking with. I use Bay Area vernacular when I'm home, southern vernacular with my college friends. My accent changes with each conversation, too. I had to develop "The Switch" as well, to be able to turn it on and off, depending on who I'm speaking with. I can't use my Virginia vernacular with cousins, they won't understand. As far as my posting on here, I often speak more "properly" in the general forums, but lean more toward AAVE with some southern slang in the Delta forum. I use a lot of my Bay Area slang in other sites I post on. I just all depends.
ETA: I don't like Dunkin' or Krispy. I prefer the local chain, Winchell's. There'll never be anything like it, so I typically don't eat donuts at all until I go home. So there.