For the average church person they might just call there Bishop by his or her first or last name. I on the other hand call the Bishop by his or her nickname. I only do this to the ones that I personally know and have to deal with it. I call these two Bish Grant and Bish Elaine. These nicknames are said by the younger people when dealing with the Bish in a conference event such as annual conference.
With my DS's, I normally call them by their first name but, sometimes I call them random things that don't really make sense unless you understand our friendship.
The looks I and the other young people get when call the Bish and other clergy said names is rather entertaining. The look is basically you just said what and he or she responded back to you. Some people think its insane that I call the Bishop or clergy anything besides his or her formal name. For me its normal and a sign of a good relationship. I think it's not a problem once you know the person and have a friendship with them that goes beyond the church walls.
In reality its not in the name of what you call your clergy, or Bish. Instead its the relationship you have with them that matters.