Well, in most communities it expands to "good game," but in MGO it more commonly expands to "git gud" and is thrown around by the snobby pro players.
... So back to Project M...
Yeah... GG def. equals "good game." Some morons on the gamefaqs forums (in the MW2) section constantly refer to GG as "get good." as you said, they usually use it in a snobby way. They think they are the best and usually just aim to annoy people by changing "GG's" meaning. To most any RTS player GG is undeniably "Good Game."
back to P:M. For the past few weeks I've been playing Jiggs as an alternative to my Falco, as she is very much opposite his gameplay. For example, she's difficult to gimp, and combo. She's a lightweight, has tons of aerial mobility, and is floaty. Again, all of these things are opposite Falco. I played her in my scrub days of Melee, and beat my noob friends. Anyway... So when I went to the S.N.E.S tournament a good number of months back, I was playing around in Melee, as I had not played it in forever. Some kid sat down, who was going to play in the Melee tournament. He played Jiggly and... I couldn't do a thing to him. Now keep in kind I'm not experienced in the arts of tournament level Melee. I understand how things work, for the most part, knowing how characters play, but as for pulling off what I see... That's anther thing entirely.
Perhaps it was the crouch cancelling that made it so hard for me to do anything against him (I was Shiek btw). If I dash attacked him, I'd get rested. If I attacked him in any way, I'd get rested. I could NOT do anything to him because I'm that bad at Melee. My attacking results in punishment. It wasn't the typical setups into rest, like pound>uair>jump into rest. It was... Me attack, jiggs laugh off the attack, standing on the ground, and resting me to death. I think CCing had a ton to do with this. It was as though he was CCing my attacks and resting when I was still overlapping his body. Can jigs in Brawl+ do anything like this? is jiggs gonna be like this in P:M? I wouldn't mind if he was, as he wasn't #1 in Melee with said strats and capabilities, I'm just wondering.