"good game," possibly or possibly not referring to a good game that has been played (or patronizing the losers), or in broader usage "good going"
Katherine: THAT WAS NOT A GG. YOU JUST BEAT ME BY A HUNDRED AND FORTY POINTS.
Bonnie: I have so much homework to do, I'm going to die. I can't believe I procrastinated so much!
Katherine: gg (good going)