Pinkie Pie woke up the next morning. She looked beside her. Sunset Shimmer was still asleep. Pinkie giggled a bit, and let out a loud fart.

Sunset woke up. "What happened?" She sniffed. "And what's that smell?"

"That was me!" Pinkie giggled.

Sunset laughed. She and Pinkie had been farting in front of each other for a while now. Sunset thought farts were funny, though she didn't make fart jokes in front of any of the other girls except Rainbow Dash. But ever since seeing Pinkie fart more around her, she was sure she was getting a fart fetish. She had told Pinkie this, and Pinkie said she didn't feel the same way but she thought they were hilarious all the same, and resolved to fart in front of Sunset as much as possible. Once, when having a major gas attack, Pinkie had held it in while running all the way to Sunset's house just to let her hear the tremendous flurry of explosive farts.

"Hey, Pinkie," said Sunset. "I was wondering... I've always wanted to try something, and I think it wouldn't be too much of a problem for me."

"What is it?" Pinkie was excited to hear what Sunset had in mind.

"I've... always wanted to smell bad." Sunset blushed a little. "Not wash for about a week or so, and wear the same outfit every day, and not wash it or my pajamas. I'm pretty sure where I work they won't notice it, and as for when we're hanging out with our friends... well, I can come up with something."

"Ooh! That sounds like fun! I'll do it too!"

"What about the bakery?"

"When I'm working there, I'll wear my dress and spray it with lots of perfume that smells like cake frosting. That way they'll smell frosting instead of me!"

Sunset giggled. "But what about the outfit you want to smell bad?"

"That'll be the outfit I'm wearing now, and I'll wear it when I'm not at work or hanging with our friends! In case you haven't noticed, I wear these to sleep too."

Sunset slapped Pinkie's butt playfully. "Then let's get started."

...

Pinkie and Sunset did not wash or shower for the next eight days. Sunset did not wash her teal tank top, jeans, or pajamas, and Pinkie did not wash her white and pink T-shirt or jean shorts, which she slept in. They didn't change or wash underwear either.

True to her word, Pinkie wore her dress at work and around their friends, sprayed with cake frosting scented perfume to mask her smell. Of course, Sunset had nothing to hide the way she smelled to her friends.

"Phew," said Applejack as she got close enough to Sunset to get a whiff of her on the fifth day. "You smell real bad, girl."

Sunset blushed. "I know. It's something I've kind of always wanted to try, and Pinkie likes me that way."

"Don't feel bad, sugarcube. There's times ah've gone for days without washin'."

They had to get close to her to smell her, and Rarity, while disgusted when she got her first whiff of Sunset, countered this by wearing more perfume.

...

On the eighth day, Pinkie and Sunset met up at Pinkie's house for another session. They both enjoyed the dirtiness of being smelly girls, and they also liked smelling each other in this state.

They had their dinner and drank some soda. Then it was time for the fun to begin.

"I know the sploshing was fun, but can we stay like this a few more days?" said Pinkie. "This is just as fun for me!"

"I'm up for smelling bad as long as you are," said Sunset. First she changed out of her stinky tank top and jeans and into her equally stinky pajamas. "So, the usual?"

"Can I rub first?"

"Go ahead. Wait, you have to spank me first."

"Oopsie! Silly me!"

Pinkie sat on a chair and Sunset went over her lap. Pinkie raised her hand and slapped Sunset's butt. Each swat stung but Sunset enjoyed it thoroughly.

After ten swats, Pinkie stopped. Sunset got off and got down on all fours, rubbing her butt.

"Hey, I'm supposed to be rubbing your tushie!" Pinkie giggled as she got behind Sunset and began caressing her rear in her hands as though it was bread dough, which Pinkie had a lot of experience with. This made the butt massage all the more enjoyable for Sunset, and her butt was as soft as bread dough.

As Pinkie rubbed Sunset's rear end, she sniffed it up close. It smelled like eight days of sweat. Pinkie sighed in satisfaction.

After two minutes, Sunset farted loudly. She giggled.

"Excuse me. You rubbing my butt forced that out."

Pinkie giggled, patted Sunset's butt lightly, and rubbed harder.

After a few more minutes, Pinkie stopped, and let Sunset take her turn.

"This is for making me fart," joked Sunset, and she slapped Pinkie's butt as hard as she could. She knew Pinkie liked to be spanked hard. Pinkie kicked her legs and screamed, but did both playfully, and Sunset knew it.

After spanking her ten times, Sunset let her get on her knees, and started to rub Pinkie's butt. Pinkie giggled, enjoying the feeling, and feeling the pain in her rear melt away.

Sunset sniffed Pinkie's tush. "Phew. Your butt smells awful."

Pinkie giggled again. "If you think it smelled bad now, get a load of this!"

PPPPPPPFFFFFFFFFFFFFT!

Pinkie giggled as she released a loud, high-pitched fart in Sunset's face.

Sunset giggled, feeling more aroused than before.

"That doesn't smell much worse than you already do," said Sunset.

"Neither did your farts," said Pinkie. She farted again and giggled. "Looks like those beans made me gassy!"

"You're not the only one." Sunset let out a deeper-pitched fart of her own as she continued to rub Pinkie's stinky rear end.

Once Pinkie's butt massage was done, Sunset sniffed Pinkie's butt deeply.

Pinkie suddenly sat on Sunset's head. Sunset let out muffled screams, but only because she knew it was more fun for Pinkie to hear a reminder that her girlfriend's head was stuck under her foul-smelling behind.

Then Pinkie farted loudly. Sunset kicked her legs, but enjoyed every second of this, and the muffled sounds she made were moans of pleasure.

Pinkie stood up and laid down on the floor. "Your turn, Sunny!"

Sunset sat on Pinkie's face. Pinkie could feel Sunset's soft, massive butt against her face, and could smell it. Pinkie kicked her legs in the air and made muffled sounds because she thought it was fun to pretend. She let out a few farts as she did so, but Sunset didn't fart on her. She wasn't quite as gassy as Pinkie.

After about a minute, Sunset stood up, and she and Pinkie took turns sniffing each other's armpits.

"Phew, your armpit smells worse than your farts," said Sunset.

Pinkie sniffed Sunset's armpit again. "Wait." She backed away a little and lifted her leg, letting out a short but loud fart. She sniffed the air around her, and then sniffed Sunset's armpits. "Yep, your armpits smell worse than my farts too!"

They giggled.

"I bet my feet smell just as bad," said Sunset.

"One way to find out!" said Pinkie.

The two smelly girls sat down and removed their socks and shoes. Pinkie sniffed Sunset's feet. "PU! You're not kidding. Your feet smell REALLY bad!" Pinkie took Sunset's foot and sniffed it up close, playing around with her toes. Sunset wondered whether Pinkie had a foot fetish.

Next it was Sunset's turn to sniff Pinkie's stinky feet. She took a deep whiff of her foot and sighed. Then she held her foot in place and started to tickle it.

Pinkie laughed, accidentally farting a few times. Sunset tickled harder, and Pinkie laughed harder.

Sunset licked Pinkie's foot, enjoying the taste of her stinky feet. Sunset was sure she had a fetish for smelly feet, but she wasn't sure if it was just the smelly part she was really interested in.

"HAHAHAHAHAHAHA! SUNNY, STOP! HAHAHAHAHAHAHA!"

Once she finished licking, Sunset let Pinkie catch her breath, and then started to tickle with her fingers again.

Pinkie laughed so hard she peed a little. She pulled her foot free of Sunset, stood up, and ran to the bathroom. She leaked into her white panties one more time before she got her shorts down, and Sunset could hear her pee splashing into the toilet. When Pinkie flushed and exited the bathroom, her shorts were a bit damp at the crotch.

"Sorry, Pinkie," said Sunset.

"It's all right," said Pinkie cheerfully. "I could stay in these all night!"

And that's exactly what she did.

Author's Notes:

I was going to put a part at the end of the fourth paragraph about Sunset wetting her jeans from laughing at Pinkie farting, but decided it would be too stretchy even by my standards.