Shooting the Bull

We've had our bull for a few years and for the first year he was really good. He hung back with the cows and kept to himself. But last year he started to get more used to his size and abilities and wasn't eager to be "handled" or walked anywhere and let me know by facing me when I wanted him to move anywhere. This spring he has given us some trouble. First he knocked down a panel fence and went out into the alfalfa for a while. I used the bobcat/skidloader to pressure him into the pasture and he challenged the skidloader the entire way. Not good if you figure that he challenged a loud steel object that is bigger than he is. Then the incident that sealed his fate occurred two nights ago. Sharon was going out in the pickup to do chicken chores in the outside part of the pasture and when I opened the gate to let Sharon drive through the bull charged the pickup and flew into a wild bucking fit. When she finished her chores and came back the bull was waiting and with head down he was mock charging the pickup. Sharon turned around and went across the pasture to a place where she could get out and climb over the fence, but the bull followed running, kicking, and mock charging the truck the whole way. It was pretty dark so Sharon couldn't see him but when she stopped and saw the bull had followed and was going at the pickup she was agitated. She finally sped across the pasture and back to the gate and I let her out of the pasture. After posting on a cattle forum that I belong to, everyone agrees that he needs to go, so I got him into the corral last night and that's where he'll live until he gets sent down the road which I hope to have done this week. I have to admit that he was very close to getting put down on the spot when he was giving Sharon such trouble. After, we were discussing the issue and Sharon said I wonder where the term "shooting the bull" comes from. I said that it definitively doesn't have anything to do with our situation...