Bibimbap in a casual setting?
It doesn't get any more fast food than the bright yellow, Korean food cart near McPherson Square metro. There's a long food cart thread on this board that gives the location. (Corner of 14th and L maybe?).
I quite like their bibimbap, though the experience in a styrofoam carton is a bit different from mixing it altogether in a nice bowl.
You can get bibimbap and a few other Korean dishes at Mark's Kitchen in Takoma Park:
http://www.markskitchen.com/lunchDinn... (has bibimbap. You can get it with meat or with an egg)
This place is owned and operated by Koreans and is walking distance from the Takoma metro.
I always order the bibimbap when I go there. It's quite casual, and you can order it for takeout.
I just saw that "the Market Place" in Ballston serves it for lunch. It is typically a food-by-the-pound place, and I noticed a long line waiting for Bibimbap at the grill. It is about 7 dollars. The address is 4100 N Fairfax Drive. I will try it out tomorrow. They have odd hours so it will be best to check it beforehand. It's located beside Caribbean Breeze.
You can get this at most large korean markets like Super H, Hanh Ah Rheum, or Lotte. These large markets typically have cafeterias that serve korean comfort food, chinese food, and even japanese food/sushi. Check out the Lotte off Rt. 50 near the I66 intersection. This lotte has those 3 cuisines I mentioned, while other Super H's that I've been to only have korean fast food. The best thing about these joints is that they serve the bean sauce over noodles, which I enjoy greatly.