Was one of my boat's names. It had no name, but we needed to have one to log in for the Fraser classic one year (2003?). Dragging it up the beach into Waddy point, we were driving past all these custom plate boats with paint jobs of bulldogs and sharks with dripping blood and lots of muscles and stuff. My mate in the passenger seat said "do you think they are trying to compensate for something?". So we called my boat "Great Big C%ck". I had planned to get a muscular looking bantam rooster painted on it to save confusion but never got around to it.
The base operator couldn't repeat our call sign without wetting his pants so he shortened it to GBC. It's been my call sign ever since.