Okay, so mine isn't so creative either...it is my initials spelled phonetically. I also have this as a carryover from trying to find an unused yahoo name. Everyone who knows me calls me "B" apparently my first name is too long and cumbersome for anyone to be bothered with saying....or typing.....
My username came about when I bought a Phalaenopsis which was mostly white but on the edges of each petal it looked like I had just finished brushing the edges of the petals with a light shade of purple . Hence the name Brush.
Ok, I'm mildly embarrased to admit that I never actually read your name properly (I had it in my mind it was something like 'quit legal' .... Hmmm, maybe I need more sleep and less OB!)
Just one of those spur of the moment "Hmm, I need a username" thing back in about 1996, so I thought "Discus fish are quite cool, I'll use that". I'm usually ahead of the "pack" in most things to get that username on most services before anyone else, so much of the time, I manage to get it and use it wherever I can. I usually have an avatar of a discus fish.