yeah, just go ahead and drink from the mysterious vending machine
"Hey Mattie, get over here quick, I just nabbed one hell of a score!" James flumped down onto his couch and dropped off a shirt-ful of soda cans to his side. "Yeah, I know right? I just like, went out of my way while going home and found some weird old vending machine. I was thirsty so I went for it, and it ate my change so I kicked it, and then it dumped like two dozen cans all at once! I had to carry them in my t-shirt just to get them home!"
James idly sorted through the collection of cans to his side as he chatted on the phone. Most things were normal enough, with a bunch of coke and pepsi and what have you, but there were a few odd outliers, things he didn't recognise from anywhere. "Huh? Yeah, I'm sure they're drinkable! Hell, these things are still cold! Okay, yeah, maybe coming over just to look at cola doesn't make sense, but there's some weird stuff in here too! Like, there's a few cans of something called 'Flamingoo'. Wild, huh? Yeah, okay, I knew you'd be interested. See you in a few!"
Hanging up the phone, James took a closer look at the bright pink can in his hand. There was plenty of fine print that was probably ingredients that he didn't care about, but more interesting was the tagline on top. 'The longer you shake, the more you take!'. "Huh, does that mean I have to shake this up before I drink it? I guess so, there's even a whole graph about the volume of the flavour or something here. Whatever, I'll just shake it a bit and see how I like it." With both hands he shook it up and down, and the similarity of his motions to a certain lewd act wasn't lost on him. He was just glad nobody could see him yet, but he was definitely going to make fun of Mattie when it was her turn to do it.
"Okay, that should be enough!" James sat the can on his lap and looked down onto its top as he opened up the pull. Instantly, a shower of pink goo exploded out onto his face and covered him all the way down to his waist. "Gah! This is some sick prank---wait, what the hell is happening?" As he looked down at his body, he realised the foamy goo was spreading all by itself, and at a rapid rate. Within seconds it had covered over the gaps that the initial spray didn't hit, and it wasn't long until even his face was hidden under a layer of the stuff. Terrified that he might suffocate, he tried to reach his arms up to wipe it off his face, but strangely enough, they were too weak to even lift. All James could do now was wait, wait until the goo finished coating his entire body, and hope he could hold his breath until then.
He gasped as his mouth was once again allowed to open once more, only... It didn't feel like a mouth anymore. Instead, it felt like he had something long and hard poking out from his face, something that curved into a dull point at the tip, and one that weighed down on his changing head. "I have a beak?!" His arms were strong enough to reach up to his face, but even they didn't feel like arms any more. He couldn't feel his hands at all, and as he moved them around they seemed to catch a whole lot more wind than they did before. "Wings, too?!"
Despite somehow having wings now, they were still good enough to wipe the last bits of goo out of his eyes, and as he looked down at his body, he gasped. "Wh---how the hell did a soft drink turn me into a flamingo?! And why is my butt so huge?!" James stood up to examine his shifting proportions, which might have been a mistake. He almost fell over as he watched his thighs gain ever more mass, as if his body was still just foamy goo that kept on expanding. The can was right, he's definitely taking on more mass after all that shaking, and as he looked under his pink tail-feathers to get a look at his sloshing butt, he could only sigh a gasp of relief at the realisation that the inflation was finally over, and that his butt was all he had to worry about.
Once turning his wobbly long-necked head back around to his front, he looked down, and realised how wrong he was. A giant horsecock as thick as his legs broke free of his overstretched trousers and flopped out in front of him as it grew to its full hardness. Its length pushed it to the point of needing James to hold it to stop him from falling off-balance, but once again, his wings were painfully useless for the task. He plopped himself back down onto the couch, his voluminous ass almost big enough to support him all by itself, and gasped from the sensation of the sensitive bumps of his cock bouncing against his chest.
The pressure building up was too much, he had to do something about it, and luckily, his neck was long enough to help him out. He reached his head down and slid the hard exterior of his flamingo beak over his flared tip, and moaned as he felt it slide into the warm wetness of his maw. Deeper down, his beak was soft enough to form a loose seal around his massive length, and once it did, he wasted no time in suckling away at his own cock.
With how sensitive his freshly-inflated cock was, it didn't take much time before he approached the edge. His wings weakly flapped against his length and didn't do much, but he was already close enough without their help. He moaned into his cock-tip as it spurted thick strings of cum straight down his gullet. The volume of all that cum was obvious from his neck bulging, what with how long it was, and soon enough, he finished up swallowing what felt like a bucket of cum and felt his belly swell with the sloshing weight of what it now carried. He almost felt like he could pass out from the pleasure of it all right there and then.
"Oh my god, James? Is that you?!"
James' eyes went wide, and he almost choked on his cock from how quickly he tried to pull it out of his mouth. "Mattie! I-I um, this isn't what, oh god it is what it looks like, I'm a freak!"
"That's nonsense, babe, you look sexy as hell!" Mattie ran over to her boyfriend and got a closer look at his mildly cum-inflated body, "Oh my gosh, you're so THICK! How the hell did this happen, and where can I get some?!"
Blushing, James pointed his wing over at the couple of cans he picked out.
"Flamingoo? Well damn, they're not subtle about this. What is this stuff, anyway?" She picked up two cans of the stuff, one with a lighter pink than the other, "Oh hey, this is the Lite version. I uh, oh, I see! This one lets you keep your arms!"
"O-oh, maybe I should've read a little closer..." James looked down at his useless wings and the complete lack of help they were.
"Yeah, I'm going to take this one. Not both of us need to be as adorably useless as you!" Mattie giggled, "So, let's see... Oh, this is interesting interesting. The longer you shake, the bigger your stuff gets! So... I guess judging from this, you went for around 10 seconds, but this chart goes all the way up to one minute... Oh my, these are some very fun numbers it's throwing around. Yeah, screw it, let's go big!"
James gulped as he watched her girlfriend begin to shake the can by spinning it around in one hand. "Weh, I can't even tease her with a stroking joke..." He said to himself. The longer she shook it for, the wider his eyes got, she was well past half a minute, and she just kept going. Her arm even started to cramp up, at which point she simply switched hands and kept going. James had no idea what she was going to look like once this was over.
"58, 59, aaand 60!" Mattie excitedly looked down at the top of the can, and just in time too, because this time the can exploded entirely on its own. A torrent of foamy pinkness overrun her body in an instant, one thick enough that James couldn't even see her body through it all. She was left inside a cloud of pink, and the only clue as to what was happening inside were the noises she made. "Oh yes!~ Nnngh, oh my god, this is incredible! I can feel myself inflating, I'm growing so huge!"
She was already large enough that the cloud of bubbles wasn't doing anything to hide her form. The extent to which her now-pink hips were swelling out was obscene, but it wasn't the only thing getting bigger. She cupped her inflating tits in her hands until the point at which they became too heavy to even carry, spilling out from her shirt until it gave up entirely and tore open. Utilising her new long neck, she got a look behind her at her equally huge ass, and instantly fell in love with what she saw.
"Oh my god, look at me now! I can't even fit through an extra-wide doorway any more..." Mattie ran her scaly yellow talon-hands over her more-than-voluptuous curves, sighing with bliss as she soaked in every iota of her hyper-inflated bombshell of a body.
"I-I am looking, Mattie, and uh..." James pointed a wing under her boobs, "I think you missed something..."
Mattie gasped as she saw a horsecock even bigger than James' grow to the point of easily squeezing through her incredible cleavage. Her old cock wasn't even as long as this monster was wide. "Holy shit... Nnnf, fuck, this thing is amazing..." She squeezed her hands over its length, her beach-ball tits helping to give it a pleasurable surface to slide through, and moaned from just how sensitive it was. "Guh, oh my god, get over here and let me fuck you, James!"
James' blushing only got brighter, but he knew better than to try and avoid Mattie when she was horny. With a bit of difficulty he lifted himself up off the couch and walked over to the other flamingo. "Oh no, she's grinning."
The moment he was within reach, Mattie grabbed his shoulders and turned him around on the spot before butting him forwards with her giant tits. Just as she planned, he landed on the floor in just the right position for Mattie to spread his ass-cheeks wide. "Mmm, you're lucky your hole's bigger too..."
Gulping, James took one last look behind him at his girlfriend's gigantic horsecock. Its tip was wider than his face, but she didn't bother letting him brace before she plunged her length into his donut-shaped hole. He moaned out, practically screaming in pleasure with all the grace of a real flamingo as he felt his insides make way for the impossibly huge cock stuffing him like a pike. Nothing should be able to handle a cock that wide and long, yet somehow, his new body could handle it. He could feel his already cum-filled belly sloshing from the roughness with which his girlfriend fucked him, and her moans made it obvious that she was enjoying the whole experience as much as he was.
"Mmmmf, oh my heck, you're so tight! You have no idea how good your ass feels, this is incredible!" Mattie was relentless as she pumped her hyper-sized length, alternating between pushing it deeper than any insertion should go before sliding it almost all the way back out and watching with delight as James spasmed with pleasure. "A-ah, I-I'm gonna, oh god, I'm gonna---!!"
James froze as he felt everything stop, Mattie almost becoming a statue, and the only evidence of her orgasm being the churning of her colossal balls bottomed out against his ass. It was like a calm before the storm, but he could already feel the storm start to pump its way through her length. The sensation of her cock expanding even further was enough to take the bullied flamingo right back to the edge he teetered on mere minutes before, and the sensation of a fire-hose of cum exploding into his belly was more than enough to make his own horsecock spasm and spurt cum too.
The inflation his belly was undergoing was already obvious, but there was no signs of it stopping any time soon. All James could do was sit there as a seemingly endless supply of spoo inflated his belly to the point of sagging all the way down to the floor, but it just kept filling up. His pink cum-filled flesh spilled out beneath him until he wasn't even kneeling. Instead, he was propped up entirely on his condom of a belly, and stretched almost to the point of being transparent. By the time the decade-long orgasm was over, the endless swirling patterns of cum floating within his belly were obvious, and it was clear that he wouldn't be getting up or going anywhere any time soon.
"F-fuck... Well, hey, at least you're now even easier to use!" Mattie let out one last giggle before flopping onto James' back and almost passing out on the spot. James, trapped under his obscenely busty girlfriend, couldn't do much to escape her, or the 5ft horsecock still stuffing his guts.
"Guh, okay, maybe I can get used to this..." James said to himself.