Nothing.
In my pre-teen years, the film Malibu's Most Wanted was released, and I thought it was hilarious. The main character, Brad Gluckman, referred to himself as “B-Rad G.” I quickly realized that because my name starts with a “G” and ends in “Rard,” I could give myself a similar nickname with the G and the B reversed: G-Rard B.
I don’t fully recall how I started referring to myself this way, but my friends picked up on it and most people never questioned it. That being said, it’s not the type of nickname that people use in any serious context; somehow, everybody understands only to use it as a joke, even if they haven’t seen the movie (this turns out to be the case for almost everybody I meet).