It's an ancient concept, they used to call it sportsmanship in the era where you took care of business the best and as hard as you could on the field during the game. Because that's when you had your chance.
When it was over, its was over, period. After that, acting like a tough guy is kind of pointless. I played in a conference championship game competing against several guys I grew up with and played from Little League through High School. I was a best man for one, and he was for me. He and another godfathers to two of my sons, and all six of us are still thick as thieves. No fans notion of how a player should act was ever going to affect that.
Kind of have to have competed at a high level, be secure in your effort, show respect to the game, and be grounded to reality to really understand it.