chess ettiquette

Saying gg after you lose is almost always okay (unless your opponent played horribly).
If you say gg after a win, some people will think you're being sarcastic or mean. So I generally avoid it. Although sometimes I will say gg if my opponent did play extremely well.

1. Saying gg is almost always alright unless you completely thrash a player. 2. Do NOT offer a rematch if you have just won. Let your opponent ask. 3. And lastly and most importantly of all, if you have decided to give up the game PLEASE RESIGN!!! And not waste somebody elses time.

Saying good game win or lose is always appropriate if it's sincere. Humble in victory, gracious in defeat.