Thanks to all, glad I managed to make that a legible post. The chapter broke me only a couple hours ago, after all. 
@will-of-R:
Your post can be a solid reference for anyone who want to argue (if they are #teamsanji) or just help to see the entire arc with a new light. Like I am now.
Thanks for posting it, hope you will post more so you can vote on AP Tournament (though you might well be enjoy reading the campaign more)
I was desperate to post something after reading this forum. Seems like a lot of people get that Sanji's having a rough time of it, but don't understand precisely what he's going through, which is amazing to me considering the flashbacks Oda's been relentlessly firing at us that make it all explicitly clear.
I will say that Sanji kicking the crap out of Luffy was extreme, but I didn't find it out of place. As many have stated, Sanji did not expect Luffy to show up at all (previous chapter had him caught off guard completely and even asking why his friends were there). He didn't have much time to sort through his options, he had to choose right then and there with Judge watching his every move. Why did he go all out and act like the bad guy? Why quit the crew? Sanji resigned himself to his fate pretty much after Zeff's life was threatened. Honestly I feel like Oda specifically drew that resignation on his face in chapter 839. He had already given up. Luffy showing up like that scared the shit out of him, because he knew if he gave Luffy even the slightest inkling that this wedding is not by his choosing, and that he needs help, Luffy would stop at NOTHING to help him. Of course, Luffy being Luffy, implicitly understood that something was still off, but to Sanji's success, Luffy is staying put which is at the very least what Sanji wants until Zeff is in the clear, or something else improves his situation.
I see some people suggesting that Sanji should have slyly informed Luffy about the situation during their brief exchange. You think Sanji doesn't know what Luffy's like? He doesn't want Luffy and the others to save him, because that would get Zeff killed. Sanji's reaction was pure desperation - an urgent last minute method of getting Luffy off his back so Zeff won't be instantly snuffed out. Sanji is a very human character when it comes to his personality, he always has been. If you're telling me you wouldn't do the same for someone you love, you're probably either lying or you're a self-preserving asshole lol. Even beyond his humanistic traits and compassion, Sanji's bond with Zeff is unfortunately entwined with his childhood trauma, which makes it more unique than just any father-son bond (and probably more unhealthy). Zeff is a man who has influenced Sanji so much that his one-off comment about not hurting women (and slitting his throat if Sanji ever does because he would become someone Zeff despises) has caused Sanji to literally become incapable of ever hitting women because he doesn't ever want Zeff to reject him like his biological father did. The fact that Sanji would go to this extreme with his own captain honestly doesn't surprise me. It's shocking, sure, but not necessarily surprising. It's very much in line with Sanji's debt to Zeff. From Sanji's perspective, no matter the outcome, he does not want Zeff to die. And he resigned himself for this reason. At least for the time being. Like I said, hopefully we'll see Sanji pick himself back up since Luffy is entrusting him with the time and space he needs.
Now as much as I get why Sanji's done what he's done, I'm just at a loss on how he will get out of this. He's still on his own for the time being. Can't wait to see where Oda will take this.
Nothing exists; even if something exists, nothing can be known about it. Even if something can be known about it,