1. B-durr is a contemporary slang term that is very similar to or is the same as durr. It is used either at the very end of a sentence or at the beginning of the sentence usually. But it can be used mid-sentence, but that's rare; unless the person talking is an air head. The longer you drag it out the last "r" (to a point, obviously) the more accentuation you are adding to your description.
2. B-durr is another slang word for "DUH"!
EX 1. B-durr! What a moron! Did you see that? He just walked into the flagpole! Hahahaha!
EX 1a. I didn't think that the test was that hard, but she didn't pass it, B-durr!
EX 1b. I don't know what she was thinking, B-durr! OMG! She just broke up with Tommy, and now they are back together?!?!? That's so typical for her to do, what an iggit!