I've always thought "BB" was a good solid sensible nick. It has the advantage that no one can shorten it to something ridiculous, and another advantage that it has no connotations. But if you don't like it, change it, I guess. As long as you're comfortable with a nick, it's your choice. I'd caution against a name from something someone else made up. One of my most embarassing ideas in my youth was to go by the nick "Mithrandir" but luckily that only lasted a few months before I wised up. It sounds to me like "Alucard" could end up being similar for you, but I could be wrong.