Being a Southern gentleman meant as much to Bones as water to a fish. It was a part of him, sarcasm and straight forwardness aside. It his tombstone read that he was a Southern gentleman, he'd be happy. (And he'd made Jim swear, during one of his more intoxicated days, that it would read as much.) After coming to grips, in his blunt McCoy-way, with his crush on the Enterprise's Communications officer, he'd set out a game plan on how he was to attempt to win the lady's heart. Leonard McCoy was no fool, and knew that the girl was crazy about Spock so it wasn't terribly likely that his plan would ever be needed.
So, four months after Spock and she broke up, Bones began reviewing his plans and thinking of ways to get the ball rolling. He settled on the tried and true approach of asking the blessing of the ex. To his credit, it showed that he had respect for what Uhura and Spock had once had between them and was not a home wrecker or poacher. To his horror, it meant that he had to talk to Spock about something other than Jim's survival and ship business.
It took him three and a half days to work up the courage to ask Spock, but in his defense, he'd seen the hobgoblin toss Jim around the bridge like a rag doll, so he thought the fear was well founded. He'd done everything he could think of to put it off further, and had even sunk as far as trying to press gang Jim into a physical exam, but he'd wound up sitting in his room and running over what he'd say to Spock. He would go, he really would. In another minute or so.
Imagine his surprise when a knock was heard at his door. Bones opened it to find Spock standing there, looking as Vulcan as ever. Straight to the point, Spock revealed that a little birdie (Thanks, Jim.) had told him Bones wanted to request his permission to court Nyota. He also said that permission was given, along with a not so subtle threat to Bones' person should any harm come to her. As he turned to walk away, Spock inhaled, and said with his back to Bones,
"Doctor, I ask only this. Love her as I cannot."
Bones watched him go, and though he didn't say it then, from that day on, whenever he was asked to characterize his ship's First mate, the first words out of Bones' mouth would be that Spock was a gentleman.
