Sanji knows. It's hard for him to believe anybody would value him that much or care that much, but he knows Luffy does. It's also why he would do anything for this man, including (but not limited to) easily going on his knees for him.

Making Luffy flustered, or maybe even managing to leave him speechless, is also another of the cook's goals. It makes him feel all giddy when it happens. Sanji hums, a pleased smile already spreading on his lips, and looks at that playful grin with interest.

"Yes, please."  It comes out a little breathless again. Their close proximity is already tempting him in all sorts of ways. It isn't easy to find a moment of privacy for them to enjoy each other; living on a small ship has that downside.  Sanji feels like he's always short on time when it comes to doting on Luffy this way.   "But now...what I want is to make you feel good."

He places a ghost of a kiss on Luffy's lips and then gently nudges him to invite him to rest his back against the wood of the shower. It leaves more room for Sanji to bow forward and place kisses on his neck and chest, and to eventually kneel down to follow with his mouth the path his fingers have trailed before.