He lays on top of you in the bed, he looks down at you with a little cute frown as he holds your waist when he says:

"I know I already asked this, buuut, why won't you call me by the nicknames I told you? I... Isn't that what two people who love each other do? Call their lover by a cute name? Yeah!"

There's a good reason why you won't call Luffy your "Little rubber boy" or "Baby Luffy". It's cringe. Even if right now you are in the privacy of your bed, imagine calling in public...