Someone who is terrible at real life and idles in World of Warcraft for days at a time begging for even the slightest bit of attention from people that he'll never meet in his life. A BDJ is typically fat, disgusting, and completely worthless in every aspect of life itself. A BDJ's only claim to fame will be any sort of "accomplishment" in World of Warcraft that not even his parents could pretend to care about.
Someone with a brain: Yo go target bdj, he just popped a destruction pot to kill that critter and is now actually posting a meter for it
Responder: Good lord what a worthless human being.
A BDJ is someone who is big and dumb and jacks (copies) other people's homework. The BDJ will pretend that he/she just wants to check their answers - but further questioning will reveal they haven't even started yet.
BDJ: "Yo can I look at your assignment, I just want to check my answers"
Me: "why you lookin at my eyes, dawg, you see some candy?"