Image imported from derpibooru 
Original Description:
 
It’s been well over an hour and Rarity has looked through every plus-sized swimwear she could find at the Carousel Boutique. As long and tedious as this was, even more so due to hefting her weight around, she couldn’t be more thankful to see that the store has finally been adding some larger sizes to their collection. It was about time too, considering that many others outside of her friend group have been looking rather big themselves. Now with a dozen two-piece swimsuits in hand, she eagerly made her way towards the dressing rooms.  
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As she hung her purse up to the side, she stared ahead past the pulled-back curtain and into the empty dressing room. Her eyes then scanned the narrow-sized door, knowing very well that she’s far too wide to just simply walk in anymore. “I’ll just save myself the embarrassment,” Rarity grumbled to herself as she began entering sideways. Even with her stomach sucked in, she still felt her fat belly and large rump rubbing up against either side of the frame. “I swear, I’m going to have to do my shopping online if I get any bigger,” she muttered as she managed to wedge herself in, closing the curtain behind her.  
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Now in the privacy of her own dressing room, even if it wasn’t as spacious as she’d prefer, Rarity dropped her swimsuits onto the side bench and began the usual routine of getting out of her clothes. She started by kicking her shoes off her chubby feet before unbuckling the tight belt that held her favorite outfit together. Freed from the most constricting parts of her wardrobe, she then slipped off her dress and top, leaving behind only her bra and underwear. Taking a moment to admire her generous figure in the mirror, she couldn’t help but sigh with relief as she felt the cool air conditioning drift across her plush body. With the weather warming up, it was such a welcome feeling.  
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But she wasn’t done just yet. Unhooking from the front, Rarity finally managed to remove her cumbersome bra, letting her hefty breasts drop freely from their confines. As she then pulled down on her underwear and let it fall around her cankles, she scanned through the pile of swimsuits, trying to decide which one to try on first. “Hmm. I suppose I can start with this one,” she said, reaching for a violet-colored one.  
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At first, she needed to take a seat just to pull the bottoms over her chubby legs, but once she lifted her body back up, they managed to fit firmly over her round belly. Next came the top, which was a bit more of a process for her. Unlike her regular bra that can be hooked up, this functioned more like a slip-on sports bra. After fitting her flabby arms through the holes, she had to tug and adjust her large breasts until they were comfortably in place.  
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She went into the shop today expecting her new swimwear to be a size too small at best. So Rarity was more than surprised by how good it actually felt to wear. As she tinkered a bit more the stretchy fabric, she decided to take some time to strike various poses and positions, watching the fat on her body bounced and jiggle from every angle she can see. “Ooh, this definitely calls for a selfie,” she gleamed as she pulled back the curtain to rush for her phone.  
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But just as she was about to reach out for her purse, she suddenly felt the narrow doorway holding her back as her fat love handles squished against the side. “Oh, dear,” she chuckled to herself as tried to take a step back inside. However, as she quickly realized that her fat body wasn’t going anywhere, her laughter slowly began to fade. Instead, her eyes widened with horror as her worst fear began to set in…  
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She was stuck.  
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Rarity huffed and puffed and heaved trying some way to free her massive body. But it was no use. As she tried to inch herself closer to her purse, hoping to at least still call for help, people were already starting to notice. Not just strangers, but classmates as well.  
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Some laughed while others just looked on with pitying eyes. All the while, Rarity could feel her chubby cheeks growing redder and redder from both exhaustion and embarrassment. It may have been a few minutes for everyone else, but for her, it felt like an endless nightmare.  
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“Don’t worry, miss!” One of the employees finally called out in an attempt to reassure her, “I’m getting some extra help to pull you out! Just don’t go anywhere!”  
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“Oh, don’t worry. I’ll be here…” Rarity replied with cold cynicism, ready to drop dead.  
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Rarity - 545 lbs  
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Please note, I heavily revised the framing to make it feel less empty, and added some blush to Rarity’s face.