Luffy unlocked it badmouthing a bull tho?
Sure, but him unlocking it premature still maintains the essence my point if you bare with me here a bit (its his affinity too unironically but that's not the point)
The only time it is officially recognized in yhe manga itself is through desperation where he let's it go berserk at Marineford.
Don't just think it will necessarily be Sanji unleashing a CoC blast out of desperation that takes out fodder in order to save someone.
CoC has already progressed from just being a tool to overwhelm people with weaker wills to a full-on attack buff.
For instance, Zoro also manifested it in the form of an attack when he first showed it on Wano. So reckon Sanji's will be similar just coz of the point we're at in the series. Is all I'm saying ^^
Let me assure you I'm not arguing just to die on this hill 😂😂, you could be correct for all Ik later on. I'm just trying to connect similitudes to make a general prediction.. induction in a sense. You bring up a neat instance with Zoro, he is the only character that has used this ability from the get go offensively (Monet moment doesn't count as an exception it remained ambiguous until zoro was recognized for the ability). Oda in a sense did what he does best is to show rudimentary affects of the ability to officially recognize it as an ability of a certain type. If you reread Zoro's moment you'd notice, when he does attain KOH form and uses Acoc, oda shows people around him getting knocked out to establish that yes it is Coc . In a sense that just adds to the general trend of people unlocking Coc in desperation yet maintaining the essence of the ability. It is Plausible that Zoro had unlocked it but wasn't as proficient at it as Luffy and kept it to some abilities like Monet, but what is important is when Oda chooses to clearly establish the ability in the manga, which was once against Kaido ( controversial and ambiguous as it was) then against King where it was reinforced and solidified.
Btw just a spit balling but Sanji's fire abilities have been evolving from jump.
We've had Diable ("Akuma" - Demon), and now Ifrit ("Majin" - High Ranking Demon) so next should be ("Maou" - Demon King) in which case we could potentially see Sanji manifesting it with that transformation
Thats a sick epithet ngl and honestly going off of how zoro got it.. Sanji might get an offensive version of Acoc it too through that. So initially it was Akuma and ifrit.. If he imbued Acoc in them it will certainly turn into a supreme version of his flames. The color or his flames could be affected by it too..Just like Sauske's chidori's color is affected by the sage chakra in his Curse Mark form.