Sabosan announces they're dating and Luffy goes all overprotective mode and won't stop telling Sabo "If you hurt my cook we will not be longer brothers, do you hear me?!!?!?!" and Sabo is like "?? How come he doesn't get threatened! I am your brother!" and Luffy is just like *shrugs* "Because Sanji won't hurt you" and Sanji gets all offended because "Hey! What are you implying?!" / "I dunno. Sanji's just too good".

And then Sanji has a crisis the whole day about it because he is still trying to see himself as a good person and then you have Sabo who is in the same boat but going "Then do you think I could hurt him????" / "No. No, no. No! But-- But you know." / "I do not know, Luffy. You're an awful liar, spit it out." / "MmmMMmMmMmm. Sabo's too reckless. You died and it hurt. And I don't want Sanji to get hurt either" / "So... The only thing I have to do is... Not die?" / "Yeah!" / "I think I can work with that, Luf."