Wait, you sometimes get banned for saying GG EZ?
Never seen a ban purely for "gg ez", but it counts as negative behaviour and is noticed as such by the system.
Ultimately it might be the last straw that gets you punished.
What if it's true?
Can't be objectively true, since it's essentially an opinion. Even if it were true, there's no reason to say it. You don't go ahead and point at every overweight person you see and say "Look, a fatty!". At least I hope you don't.
If you don't have anything nice to say, sometimes it's better to just not say anything at all.
if it's sarcastic?
That can be used as an excuse for pretty much every kind of negative behaviour in chat. Ultimately, if you want to make a joke based on something that could offend people, you have to make sure you communicate that in a way that people understand it.
Sarcasm in plain text is difficult to apply. Saying things like "j/k" helps.
Is gloating not allowed?
A bit of a too general question, but ultimately the answer is no.
Show grace in defeat and humillty in victory.
Yas top playing the broken champ of the week spamming his level 7 mastery for the first three minutes where he dashes through me till' I first blood him and I can't even reply with a GG EZ?
Exactly.
I bet you'd never get banned for saying "Good game, that was easy"
Why wouldn't you? It's not that common a phrase, so the system might not pick it up immediately, but it's the same idea.
But as said... getting banned purely for saying "gg ez" (or "Good game, that was easy") is pretty difficult.