Similar to many other 'meister' names, 'g meister' is most commonly used as a nickname of endearment with the 'g' often being the individual's initial.
Although, 'g meister' specifically, may also pay tribute to 'Game
Master', (or
even 'Dungeon
Master', as Dungeons and Dragons refference) as the direct German translation for 'meister' is 'master'.