A player's courtesy to the people he can get away with being nasty to (i.e., the non-millionaires who stare at lines so that the players can enjoy the limelight) always makes a strong impression on me.
There's a famous story from the 30's
of Don Budge, in a big win, giving his favored opponent a free point in response to a bad call. Afterward, Gottfried Von Cramm, one of the sport's all-time great gentlemen, suggested to him that his behavior was incorrect for having embarrassed the linesman. I read in another account that Budge regarded the conversation as an important lesson.
Whether or not one agrees with Von Cramm, the essence of sportsmanship is stopping to consider the other person, and by that standard this was a higher level of it.