I decided to write my own prediction of how Sanji's wedding ceremony will go...I'm not trying to accurately predict what'll happen, I just had some fun writing this little piece. So enjoy.
A Mokomo Dukedom ship docks at Whole Cake Island. Out steps Pekoms, accompanied by the Straw Hats who wear fancy tuxes and dresses and whatnot, and they each have headgear covering their faces.
Pekoms: All right, I took you here, but you're on your own now-gao! I have no wish to be involved in your suicidal plot!
Luffy: Why'd we have to sail on that uncomfortable ship???
Zoro: We can't just dock the Sunny here and not have anyone recognize it! Law and the samurais are keeping it safe.
Nami: All right...everyone's disguises on? Everyone's got their fake invitations?
The Straw Hats flash their invitations, forged by Pekoms against his will.
Robin: Wait...where's Raizo?
Robin gasps as she forces Raizo out from under her skirt.
Robin: Don't ever do that again!
Raizo: But I don't like being out in the open like this...I need someplace to hide...
Nami: Samurai... shakes her head
Usopp: So, we all know the plan, right?
Luffy: Yep! Raizo's gonna sneak me in for me to steal Sanji, and-
Some of the guests' heads turn, and Franky holds his hand against Luffy's mouth.
Nami: Not so loud you moron! First we get into the palace!
The Straw Hats walk toward the palace gates, with Raizo taking refuge in Zoro's trenchcoat.
The Straw Hats hold out their invitations. The guard examines them, and waves them in.
Nami: All right, we're off to the wedding hall. Go, Luffy and Raizo, and whatever you do, do not talk to anyone.
The Straw Hats turn a corner, and Luffy keeps going straight. Raizo follows him, dashing quickly from one object to another so that no one can see him.
Guest: Who's that weird dude?
Raizo: Luffy! There's a vent under this table here!
Luffy notices it and crawls under the table. Raizo has already gotten it off, and he and Luffy climb inside.
Meanwhile, Sanji is being attended to in a nearby room. He is decked out in a tux as he has gone through the process mostly silently. However, a scuffle begins when the attendants try to do his hair.
Sanji: No! Don't part my hair like that! I don't want both my eyes showing!
Attendant: Mama doesn't like hair unkempt like that...don't resist!
???: It's all right, gentlemen. Leave his hair be; it's a sad pirate trait of his.
Sanji: So...you're here, father.
We get a full glimpse of Sanji's father, Machi, a tall and skinny man in his mid-fifties, with graying brown hair. He smokes a pipe as he walks toward his son.
Machi: Tut tut, Sanji, a child's marriage is a father's greatest moment. Even if the child hasn't been seen in over ten years!
Sanji: I have nothing to share with you...but I would like to ask. Why did you tamper with my bounty just to arrange this marriage?
Machi: I have no reason to tell you that. I have no interest in you after the ceremony is over, you'll be left in Big Mom's hands. I only want the marriage to go through so the Vinsmoke Family and the Charlotte Family can become one!
Sanji: Good. The less time spent around you, the better.
Machi: That's too bad...it'll greatly hamper my best man's speech at the reception...speaking of which, would you like to meet the groomsmen?
Second Vinsmoke son Niji runs up to Sanji and tackles him in a bear hug. He has a much larger frame than Sanji, and the force of his hug knocks the wind out of Sanji.
Niji: My baby brother's all grown up! Feels Sanji's arms Man, your arms are so spindly! I'd hoped you'd be better at arm wrestling now...
Sanji: Get off idiot!
Sanji kicks Niji in the stomach, which knocks the wind out of his brother and sends him reeling back.
Niji: Oooh, so that's why they call you "Black Leg!" Ya saving your arms for the kitchen or something? That's a woman's job, little brother!
Sanji: Shut up.
???: Now now now...we can't be fighting after we've just met, can we, brothers?
Before Sanji can react, the eldest Vinsmoke son Ichiji clamps his arm around Sanji's neck, as he did many years ago. He is a mix between Niji and Sanji, boasting a body both strong and agile.
Sanji: Haaah! Get...off!
Ichiji: Man, you're no fun...you're just as wimpy as when you were five!
Sanji's eyes begin widening and he sweats and trembles in fear.
Sanji: Please...I beg you...
Ichiji: Say uncle!
Sanji begins breathing harder, before he lets out a roar and rear-kicks Ichiji in a painful area. Ichiji falls to his knees, rage flaming in his eyes, and gets up and rolls up his sleeves.
Ichiji: You wanna fight, San? You wanna go "there?"
Sanji: You don't intimidate me anymore, shithead!
Niji: Oh boy! I love myself a good brawl!
Sanji and Ichiji head toward each other, ready to lay a smackdown, when suddenly someone else gets between them in the blink of an eye.
???: Stop. Now.
Yonji, the fourth son of the Vinsmokes, stares at both his brothers. Despite being only 13 and well shorter than his siblings, his look gets across clearly to them.
Yonji: Don't ruin this ceremony. Or I'll kill both of you.
Yonji's words have a real threat behind them, and both Sanji and Ichiji step back in a cold sweat. His work done, Yonji heads out the door.
Sanji: The last time I saw Yonji, he was a baby...what on earth did he turn into?
Machi: Well...we've had enough reunion for now. The ceremony starts in a half-hour; we'd best leave Sanji enough time to be made somewhat presentable.
Ichiji and Niji head out, but Sanji calls to his father as he begins to depart.
Sanji: What on Earth did you do to Yonji?
Machi: I see no reason to tell you, given how little you've cared about him these past 12 years.
Sanji: Your underworld bullshit corrupted him...Ichiji and Niji are fools, but Yonji is a monster, all because you didn't let him have a mother-
Suddenly, Machi rushes forward and grabs Sanji by his collar.
Machi: None of you had a mother. Don't you ever get those thoughts in your head again, DO YOU UNDERSTAND ME???
Machi releases Sanji and storms off. Sanji holds his head down, looking grim.
Meanwhile, a select few members of the Big Mom Pirates sit at a dining table in the ballroom, engaged in some pre-ceremony cocktails. Big Mom takes up an entire side of the table, while Bobbin and a few other shady-looking people sit around the corner. Directly across from Big Mom sit some of her special guests, including Capone Bege and Jinbe.
Jinbe: I haven't seen the Straw Hats anywhere...it'd be suicide, but it wouldn't be like them to not come and try something stupid...
Bege: I must say, Mama, this particular tea is exquisite.
Big Mom: Oh, you're too kind, Bege. This doesn't compare to the drink I'll be serving at the reception, of course. The people of the island of Kamomiru were gracious enough to serve their legendary brews, free of charge!
Pirate: Mmmm...my crew and I love coming to these weddings!
Big Mom: It's been too long since I've thrown one...but I can't believe my 35th daughter's getting married! I seems just like yesterday that Bege married my 34th, Taruto! I trust everything's going well for the two of you?
Bege: Er, yes...we're very happy.
Big Mom: I should hope so. And you, Jinbe! I must say, I wasn't too pleased with your people a few weeks back. Luckily, they compensated nicely with that treasure. I'll still be going after that no-good brat Monkey D. Luffy, especially after his crew damaged my dear ship, but I've got a wedding to worry about first. And what better way to decorate a reception than with Fishman Island's finest treasure??
Jinbe: Crap! If there's an active bomb in that hoard...it might be best if the Straw Hats steer clear of here. But then...what'll happen to my people...? I've got to eliminate the bomb somehow, even if it costs me my life!
The Big Mom Pirates turn their heads to see the injured mink arrive. Pekoms looks at Bege, but the Supernova only glances at him expressionless before turning away.
Pekoms: I'm royally screwed if he told Mama what I did...but I can't turn back now!
Big Mom: Ah, Pekoms! Bege told me your tribesfolk kidnapped you. He tried his best to save you, but it seems you've escaped on your own.
Pekoms glances at Bege again, trying to conceal his shock. Bege pays him no mind.
Pekoms: As much as I wanna say what that scumbag did...it would certainly screw up the wedding, and Mama wouldn't like that! Also...if I say what he did, he might spill the beans on me too...and what if Mama takes his side? Oooh, I won't forget this, Bege!
Pekoms: Yes, mama. My tribe held me hostage, but I escaped from those fleabags-gao!
Big Mom: I was hoping for you to be the ringbearer, but those wounds don't look sightly at all! I'll use the backup instead. Tresse!
A male dwarf, nearly a speck compared to Big Mom, dashes toward the table and races onto it. He trembles in fear as he faces Big Mom, like he always does.
Tresse: W-ww-w-w-what i-is it, m-m-mlad-lady?
Big Mom: I want you to be the ring bearer for the wedding. Just stay cute, like you always are!
Big Mom scoops up Tress with a hand and presses him into her chest for a hug. His trembling increases significantly, but he withholds squealing in fright. Bad things happened to him if he did that.
Tresse: R-r-right a-away Mama!!
Big Mom: Better get moving, people! We've got a wedding soon!
Meanwhile, Law and his crew lounge about on their submarine, with the Thousand Sunny docked nearby.
Bepo: I still don't understand why we can't go to the wedding. I want some action!
Law: Knowing Luffy, I'd be surprised if nothing came our way. It's our job to keep their ship safe. Remember, this was never an agreement for our alliance.
Kin'emon: I hope our comrade Raizo will be safe...he's been through quite a lot of Yonko-related matters recently!
Suddenly, Law notices a ship sailing nearby, and he instantly recognizes the Jolly Roger.
Law: Oi! Cabbage!
Cavendish looks for the source of the shout. He sees Law, makes a disgusted face, and turns away.
Cavendish: What're you doing so close to Whole Cake Island, Trafalgar? I thought you were starting shit with Kaido, not Big Mom!
Law: I just go where my heart takes me. You headed to the tea party?
Cavendish: Sighhhh... Yes. I have no desire to go, but someone neglected to tell me a bit of his extra baggage!
Suleiman: I've had some dealings with the Vinsmokes in the past. I didn't know they got involved with Big Mom until I got the invitation.
Cavendish: I'm running background checks before I let anyone else into the crew! Say...isn't that the Straw Hats' ship?
Law: Yes, but they're not here right now.
Cavendish: Wait. You don't mean...pulls out his Vivre Card HE'S AT THE WEDDING??? HE'S GONNA RESCUE BLACK LEG FROM BIG MOM???
Law: I'm afraid so. But Cabbage, before you go...would you mind shooting a message to the other Grand Fleet crews.
Cavendish: I already know what you mean. I'll do that...as things are unlikely to go much better.
Later, the wedding hall is packed to the brim with guests. The minister stands at the altar, along with Sanji, Machi, Ichiji, Niji, and Yonji. "Here Comes the Bride" begins playing, and the doors at the back burst open. The only thing most people can see is Big Mom towering over them, and most tremble in fear.
Usopp: Damn, that's Big Mom? She's so frightening!
Franky: I hope Luffy's OK...I certainly don't want to draw her attention!
Big Mom leads Purin down the aisle. Purin is of very short stature, standing well below most of the guests, barely reacheing Big Mom's waist. Her face is shrouded in a white veil. Big Mom leads Sanji to the altar, and takes her seat on a couch behind the altar.
Minister: Mawwage. Mawwage is what bwings us togethew today...
Meanwhile, Luffy and Raizo crawl through the air vent.
Raizo: Luffy! There's an opening here. We're directly above the altar!
Luffy: Great! So, the plan...you hold me, and I'll reach and pull Sanji up here! Then we run!
Raizo: Yes...who made this plan, by the way?
Luffy: I did. Why?
Raizo: Oh boy, this is going to go so well... OK Luffy. Open the grate, and don't make a sound.
Minister: Now fow the vows...the gwoom may unveil the bwide.
Sanji grimaces as he slowly lifts up Purin's veil. When he flips it over and looks at her face, he looks visibly shocked and lets out a small gasp.
Purin: Hey there! You look as cute as I thought!
Sanji: How old are you?? Twelve???
Big Mom: Quiet!
Tresse runs forward as he hands over the rings, though nearly drops them several times due to his constant trembling. As the vows begin, Luffy looks down into the hall, having removed the grate.
Luffy: They're doing the vows now! Grab hold of me, Raizo, I'm going in! Gomu Gomu no...
Raizo: That three-eyed girl...if only Kin'emon could see...wait, WAIT! I wasn't ready!
However, Luffy doesn't hear him as he throws his arm down toward Sanji. However, he has placed most of his weight into thin air, and without Raizo grabbing him, gravity takes effect. Luffy follows his arm down into the wedding hall, screaming all the way. He lands on the minister, sending them crashing to the ground right between Sanji and Purin.
And, as a great author once said, that was the moment the shit hit the fan.