Can I get banned for saying GGYFSA?

We both know you know what is ok and what isn't. Is it negative? Yes. Will you get banned for saying that once? No, that's not how bans work. Can you get banned if you keep doing it and are being reported consistently, especially after prior chat restrictions? Yes, that is how bans work.

Is it necessary? I don't see whats wrong with simply "gg" then move on to the next game.

I think that would fall under unsportsmanlike conduct, so yes.

Try gg with racial slurs after

I'd stick with just "gg"....

GGYFSA is probably fine as long as you never tell anyone what it means, since if they don't know they'll generally give you the benefit of the doubt.

Better idea, just make all of your chat in game acronyms. First letter of every word. Never clarify.

You're toxic. End of story, so yes, you deserved it.

To quote Sky Williams...

"Hey, here's an idea. Just don't."