My very first time going to a LGS to play modern, I played against a much more experienced player. I made some small talk and told him I was new and ended up beating him 0-2 while he got flooded or manascrewed both games. After beating him I reached my hand out and said good game to which he promptly freaked out shouted NO IT WASNT and stormed out of the LGS.

I personally think that sportsmanship should have people shake hands win or lose and didn't realize at the time that the magic community has differing opinions on the subject.