No Different
It wasn't unusual. Not for people as close as a first mate and a Captain could be. Or at least, the rest of the crew didn't think it was unusual, when they saw Luffy challenging Zoro to a match that the swordsman would most likely lose.
Of course, Zoro would never back down from a challenge, lest of all one that Luffy boasted he could beat the swordsman with one arm tied behind his back… literally. And when Luffy did win, Zoro would challenge Luffy right back, and then it started all over again.
It was no different at night, when the rest of the boys were asleep, and Luffy would pad silently over to Zoro's bed, whisper in the swordsman's ear and then climb into the hammock with him. The whispered challenges, and the gasped names, was something the other men of the ship had had to learn to ignore.
And when the morning came, and Sanji snuck his way into the kitchen, the chef silently thought that no, there wasn't a better pair on this ship except perhaps… Nami and himself.
Shit… burnt the frigging bacon again.
End