It's funny stuff.
You're all getting to know the generation that will destroy civilization out of hissy fits.
It's what happens when you breast feed your kids until they're 7.
I'm pretty sure the phrase "good game" predates online gaming and is a part of sportsmanship that does not mean "I enjoyed the game and you didn't ner ner".
What made it "good" is the fact you had a worthy opponent who took the time to play with you. It's just respect. If anything, not saying gg should be what is offensive.