What does GG mean ???

GG depends.
Sometimes it means "Ha ha! You lost! You are a total newb! I pwned you!"
Then, other times, it means "Good game. Well played. I hope we play again sometimes."
Or it could be some combination of the two.
Or neither of them.
Gg can be tricky. You really need to pay attention to the context.

I use gg as a thanks for the game and all. Win or lose. I didn't realize people could take offense to it. That seems outrageous to me.
<<Ramble On>>
But I think that sarcastic and negative people may take offense to Good Game because they think it's a snide remark . . .much like one they would probably make. It's like a person that lies alot usually assumes someone else is lying, because it's what they do to others.
I appreciate any game I play. Ones where I get my a$$ kicked or one I control the whole way because I learn one way or another. I remember being a poor chess player (not that I'm all that now) and appreciating the times good chess players stopped down to teach me.
<<Ramble Off>>
When I re-read this thread earlier I realzed that one important GG was missing, that is funnyman George Gobel. Gobel had a long career in Entertainment but is probably best remembered today as a regular on the original " Hollywood Squares ".