I am convinced some people here are from a different planet . How can saying good game be considered rude ? It is literally the winner showing humility and acknowledging that the other guy played well , even though he lost that particular match. What is this world coming to , where people are so wound up, that saying good game is considered an insult ? Next, you will say that saying "hello " is rude
That's how people are these days, and that's a pity.
Someone else's existence is rude, basically. Someone else winning a game is double rude.
I think it's rude to insist on a draw from a winning player. It isn't rude that chess is a competitive game, where there are usually a winner and a loser. People who don't like that should not engage in a game like that. If they only love the other elements of chess but not the fact that it's competitive, they should solve puzzles or something like that.
Lots of people say "haha, I won", or "you're gonna lose this", and even that is not rude. Cocky, perhaps, but not rude. It's totally okay to be cocky in a game that is essentially a duel of minds. It's not something malevolent.
Speaking of that, I had an opponent, who at some point of the middlegame started saying to me "loser". When I reacted by an innocent question, he went on - "loser", "you're gonna lose", etc. Meanwhile, the game was very equal - I think he had a +1 advantage resulting from a book opening, and that was all.
Then he performed what he probably thought was a cunning trap. He had me struggling for a couple of moves and send me the picture of an eggplant. Then I took his rook and gained +4 advantage. The game was nowhere close to finished yet, but he abandoned the game and lost on time. He also removed me from his friends, blocked me, and refused from rematch. (Perhaps he also reported me and whatnot, but there's no way for me to know.)
I think that's rude, but I didn't feel offended. It seemed he was the one who somehow got offended.
To answer the actual question of the post, no saying gg is not considered bad.
Some players react negatively to you typing GG and it is usually when they have lost and are angry, and seeing a GG pisses them off.
that doesn't mean saying gg when winning is considered bad. The term good game is a sign of good sportsmanship, and this is recognised in both sports, and video games, and it is the same for chess.
That's all. nothing more, nothing less. a sign of respect.