I didn’t play sports when I was younger so maybe there were some sportsmanship lessons I missed during my upbringing.
I did however play a lot of video games. Starcraft among others, and I believe this where saying “gg” originated. If one quits a game before it completes it can be seen as “ragequitting” which is definitely unsportsmanlike. When one is in a hopeless position in this game and wants to resign and not be perceived as ragequitting saying “gg” before quitting was the norm. So the winner saying “gg” seems awkward to me, if not disrespectful. But I see nobody here agrees so I’ll just accept that I’m just out of touch.
I’ll add though that despite not having any sports experience I have quite a bit of live poker experience. And my impression from years of playing is that the best etiquette for the winner of a pot is to say nothing. I find any remarks or celebrations made just after the hand by the winner disrespectful. Unless it’s an apology for sucking out or something along those lines. The loser is free to make remarks, and the winner should be expected to tolerate a small amount of flack, but is free to respond if spoken to. But again that might be just me.
