Trying to toughen up my 9 year old nephew

Good guy aunt/uncle

At first all I saw was "I beat my nephew mercilessly"

I do the same thing.

I have a friend that will give up playing if he loses. It pisses me off

Yeah my nephew is a bit like that too. He'll try to quit or start trying to cheat if he isn't winning, and his parents can't play games worth a damn but his father is super competitive with sports, which doesn't help. I can still beat him for now, but I won't be able to for much longer, he'll be a teenager and I'll be in my 50's. I hope I can still keep him from being a complete ass.

Good.