When Luffy brought the question up, Sanji was a bit confused.
"What would I cook for an enemy? Why are you asking me that now?" He looked around, trying to see if he was missing something. Noting that nothing was out of place, he looked back at the captain.
Luffy cocked his head to the side, and looked at him thoughtfully. "I've just wondered it for a while, that's all."
Sanji took a deep drag from his cigarette while he decided between kicking his captain in the head, and giving him a real answer. When he finally chose the latter, he closed his eyes and exhaled slowly.
"I'd feed them exactly what I'd feed the crew. Everyone always deserves to eat, no matter what."
Luffy nodded slowly for a moment, then grinned widely. "Okay!"
Sanji just shook his head as the bouncy captain quickly walked away.