I will make a concious effort to be more courteous to my opponents from here on, and treat them as I wish to be treated. I'm not a rude person by nature, it just hadn't occurred to me to wish my opponent luck and acknowledge defeat with a 'gg' at the end.
I agree entirely with the saying gg and playing on sentiment being incredibly bad mannered, as well as the saying gg for your opponent when you've clearly won. It's just not good sportsmanship, and I'd be pretty frustrated if it were done to me.
rofl