I had a girl trying to rush me through my turns half of our game. The funny thing is that I'm usually fairly quick with my turns, but she kept saying, "please hurry." "Please hurry."
So I started to go slower...and slower...
hehehe

I start with "gl" and end with "gg" no matter how it ends. I had a VERY good competitor today and it was a terrific game. At the end I said, "thank you for a great game" and he said, "yeah, go to he'll" Not really much more to say there.
As for "hehe, LOL" during a game, I agree that it is ok to be excited about a good move you may have made, but I don't think it is necessary to type those thoughts out on the screen. Sometimes, however, if the mood is fitting between the 2 players, this can be appropriate to some degree. For example, I was in a game in which someone made a move that trapped my king. I said, "nice move" and he replied, "hehe thx." I had absolutely no problem with this as the context it was in.
While we are on the topic, I was in a game today that was clearly me against another player AND his friend who was telling him IN THE ROOM every move. His friend also would rush me and "remind" me of the timer EVERY turn. I was not going to quit and give him the win, but I did comment, "If you would like to play 1 on 1 against me sometime, let me know." I think he and his friend were rude and completely inappropriate.
There's a lot of new 'etiquette" to be discovered in checkers, that's for sure.
Perhaps it was someone who never played checkers before? I played against a friend who during the game told me he never played checkers ever before so didn't know how normal checkers worked.
As for good sportsmanship....how can we expect it from kids nowdays when the professionals (football, hockey, baseball, etc etc) get away with their poor sportmanship..but that's a whole other subject. They could ALL learn good sportsmanship in my opinion (stepping off of soapbox now)