To be honest, I would say that an incorrect usage of "gg" is not the criminal offence you make it sound, far better that than getting sent proper abuse! Also there is the case that the player is just trying to be friendly, and perhaps suggesting that the rest of the game up to the blunder was well played. But if it upsets you, just block them. Problem solved.
Good Game? then what do you mean by gg?

I rarely say anything. If a game was really fun, lots of complications, result up in the air for a long time -- then I say "good game". If it was really really bad, blunders for both sides all the time, and I somehow won in the end, then I sometimes say "bad game :-)".
I can't recall any "worst experience". Why remember someone's stupid comment?

I disagree that it is inconsiderate or arrogant to say "good game" after a decisive victory. I interpret "gg" as the online equivalent of shaking hands after a game OTB. I feel it would be poor sportsmanship for the loser of an OTB game to refuse to shake hands, and even more disrepectful for the winner to refuse; dismissing the game as not up to his or her standards.
As an analogy, even when a top ranked tennis player wins in straight sets against a far lesser opponent, I expect them to shake hands after the match.
I recognize that not everybody uses the phrase in the same way, but I think many people do. If you infer too much from a simple "gg", I fear you will be misrepresenting a lot of players who are only trying to thank you for a game played honestly and to the best of both player's abilities.

Generally I've become to lazy to type any comments at all, unless someone types something worth responding to.
I probably look like an ass, but what does it matter?

If it WAS a good game, I'll write gg. If it wasn't, or my opponent played poorly, I'll just say "thanks for the game."

well. if you want to be literal.
If it was not a "good" game, why did you play?
let's say you make a cirippling blunder and essentialy lose the game and you feel there is nothing to be gained by attempting to recover then just resign. If you continue to play you must feel there is some value to the game.
ok, so that seems obvious.
how about if your opponenet makes the blunder but continues to drag out the game. why don't they just resign already? well guess what, they must feel that the game still has some value to them.
let us be clear what good means. good just means there is some benifit. it just means a net positive. It doesn't have to be an "awesome" game or "great" game.

If the game was a one sided crushing (on either end) I will say thank you for the game. If the game was a "good game" I will reply as such. I do this in any sport, or game I play, over the board or online.
I don't use "gg." I spell out "Good game." The "gg" seems too perfunctory to actually be good manners.
well. if you want to be literal.
If it was not a "good" game, why did you play?
let's say you make a cirippling blunder and essentialy lose the game and you feel there is nothing to be gained by attempting to recover then just resign. If you continue to play you must feel there is some value to the game.
ok, so that seems obvious.
how about if your opponenet makes the blunder but continues to drag out the game. why don't they just resign already? well guess what, they must feel that the game still has some value to them.
let us be clear what good means. good just means there is some benifit. it just means a net positive. It doesn't have to be an "awesome" game or "great" game.
I usually say good game when I lose. But in regards to when I am down after a big blunder, I always try to finish the game. Maybe my opponent wants to practice the end game.

I too don't like seeing gg after a bad game, I don't like it even if my opponent does the blundering and I win the game it certainly wasn't a good game if it was one because of a gross blunder.
Other things that I don't like is "good luck" at the start, and people that play on in hopeless positions.

lame. its been a very long time since i played serious OTB chess, but even in skittles games it is obligatory and proper to shake hands and acknowledge your opponent before and after a game. even if nothing else is said between the two of you in-between the first and last moves, its just good manners to say SOMETHING. gl and gg are the lazy mans manners online. although i do like the idea of SH and TFTG but im not sure how many people are familiar with these acronyms. manners are quickly disappearing from culture and this forum clearly expresses the general trend toward impersonal interactions devoid of common courtesy. its sad that online strangers get angry when someone is trying to display civility. sad indeed.
i am just going off my own experience in live chess games, but it occured to me that the acronyms 'gg' are sometimes used in direct contradiction to what they stand for; 'good game' and as a show of good sportsmanship. i must first make it clear though that the majority of people i encounter do use it correctly and i thank them for that. but that small minority really bugs me.
personally, i only say gg after a mutually well-played game, irrespective of a win or a loss, hence the 'good game'. for instance, if i win after a series of extraodanary blunders on my opponents part, i am not going to hit the double g's. likewise, if i lose after pathetically leaving my queen open to a hungry bishop, there is not a chance of me claiming it was a good game! not that it was my opponents fault, it was clearly mine; but mistakes and blunders do not make for good games.
i've noticed that occasionally there's an opponent who will hastily type gg as soon as they win a game such as the ones above. what must they be expecting as a reply? a gg in response? a yes, you played very well?
i was left dumbstruck by the inconsiderate attitudes exhibited by these players, yet simultaneously intrigued to find out how other players would respond
to this kind of behaviour. no, i did not start a post asking what others would do, nor did i create a poll. i wanted a first hand account of how players out there responded to this kind of arrogant and inconsiderate behaviour. so i proceeded to play bullet chess until i beat a player of similar ranking after he/she had made an erroneous move. as soon as the "white won" sign popped up, i went for it: gg.
how did they respond? well, i only experimented on 3 different users, a) because it takes a long time to find a similarly ranked player who seriously screws up a game and b) i wanted to minimize offending unsuspecting individuals. the first player responded with an intentionally misspelt expletive phrase, which i wont repeat, while the second & third players did not respond at all. i didnt see any of them again, and i assume they blocked me.
i dont know if this is a premature conclusion for me to make, but do some people consider a game won due to the mistakes of their opponents, and not overwhelmingly due to their own brilliance, to have been a good game?
and more generally, do more people say gg when they win than when they lose?
once more i must reiterate, irrespective of a win or a loss, there are many who do properly and justifiably claim gg. i have had quite a few memorable conversations that were initiated by a sincere gg expressed at the end of a pleasent game of chess by either me or my opponent. it is just those who claim that a game in which either player seriously stuffed up to have been a good game that bug me.
also, what is your worst experience of a misused gg? mine was in a bullet-chess game where in the late midgame i blindly positioned my queen on an undefended square and lost it to a knight, which then just happened to fork my king and rook...dumb move by me but what can you do except resign when you add to the list a looming queen and a rook with an open file staring hard down at ur king? two or three seconds after i hit resign, a message appeared from my opponent:
"ggg"