A shorthand version of the name Gary Motherf****** Oak. The name is used to
represent a rival who one-ups you at every conceivable instance, as Gary Oak did to Ash (or as his
counterpart did to the player character in
Pokemon Red, Blue, Yellow, Fire Red, and Leaf Green).
You just
defeated Lance, with only one pokemon left and no more revives. You're ready to be declared
Champion, until Lance reveals that
someone else has already beat him: GMFO.