"A... What?" You cock an eyebrow at Rainbow Dash, she's definitely caught you off-guard.
"A gross-off dummy!" She said, looking at you like you're the crazy one, "I knew the moment that you'd blasted that burp in my face that you'd be perfect for a gross-off, it's a Ponyville tradition!"
"Oh well, if it's a tradition then I..." before you could finish, Rainbow says,
"Good!" and dashes off. She was only gone for maybe a few minutes, but with her speed she could have covered half of Equestria in that time. Ten minutes pass, and you end up sitting down on the road waiting for her. Eventually she comes back, but she's walking now, beside a white unicorn who seems to have no problem taking her sweet time getting to you.
"Sorry for the wait," Rainbow Dash says, "but to have a gross-off you need a judge, and the only one with a nose for gnarly smells here is Rarity. As you can see, she doesn't like to run anywhere."
"Excuse me Rainbow darling, but I will not allow myself to become sweaty. I cannot let my personal body odor corrupt the smell of you two." The unicorn says, before turning towards you. She extends a hoof and says, "Rarity, it's a pleasure. And you are?"
"Orange Crush," You say, "But I really have to know, Rainbow Dash, what is a Gross-off?"
Rarity seems shocked, "Darling, you don't know? Why, that's an utterly shameful display! How could you hope to win?"
Rainbow Dash laughs, "Oh, I don't think she should be worried about that! I told you about her nasty belch, right?"
"Well I suppose," Rarity said, "But still, we have to cover the basics. Orange dear, the contest is a test of skills that disgust most ponies. But amongst certain circles, they're looked upon highly. There will be five rounds, of which you and Rainbow Dash will perform uncouth, disgusting acts on yours truly. The loser of each round must endure the same treatment from the winner, and the majority loser will experience each five again. Are we clear?"
You nod, and Rarity points her hoof towards a small meadow near town, where she tells you the contest shall take place. You and Dash run ahead, and Rarity takes her time getting there, but soon you're all there, and you can begin. Rarity pulls a small cape from her saddlebag and drapes it over her shoulders, looking quite queenly in the process. She takes a seat in the grass and says,
"It is time to begin. Are the contestants ready?"
"Ready!" Rainbow Dash yells. You just nod.
"Excellent! Now let us begin! Our first challenge will be hoof odor! Orange Crush, as our guest you may begin."
You look to Dash, and she impatiently gestures her hoof toward Rarity, who has her eyes closed and her nose pointed toward you. You hesitate, but you eventually turn and stick your back hoof toward Rarity's nose. She starts taking hungry sniffs of your hoof, which is still sweaty from all the walking you've done to get here.
"Oh! Rancid! Utterly disgusting!" Rarity says, happily, "Dank tones of dirt mixed with sweat, I can tell you are a pony who likes to hoof it from place to place!"
She pushes your hoof away and then ushers Rainbow Dash forward. Rarity sniffs her hoof, but looks very disappointed. It must be because Dash spends so much time flying and not walking. She pushes Dash's hoof away and proclaims the victor,
"Round one goes to Orange Crush! As penalty, Rainbow Dash must take three licks of both of her back hooves."
"Aw man!" Dash says. She gives you a grouchy look, but she can't argue now. You sit and present your back hooves, delighting in the sensation of her tongue cleaning the sweat and grime off your soles. She finishes the job, and looks sick.
"I don't think I'll ever get that taste off my tongue," Dash says begrudingly, and you can't help but laugh.
"Round two!" Rarity says, "This round will be legpits! Orange, for winning the last round, you will go first again!"
You approach, and Rarity lifts your foreleg up, burying her face in your sweaty legpit. You think you feel her licking inbetween sniffs. Rarity pulls back with a blissful look on her face and gives a contended sigh. Dash goes next, but instead of offering Rarity her legpit, she extends her wing so the unicorn can sniff her wingpit, which is dripping with sweat. Rarity eats it up, literally that is, she slurps up enormous gobs of Dash's sweat. Finally she seems to have had her fill,and announces the winner,
"Round two goes to Rainbow Dash! As punishment Orange Crush will suffer a ten second reverse headlock!"
You don't have a second after that to think, Dash tackles you and stuffs your head into her equally smelly legpit, covering your face in sweat. You're briefly reminded of the time you tried Extreme Pony Roller Derby while trying to get your Cutie Mark as a foal. You were so terrible that the team forced you to scrub their gear, Dash's pit smells worse than a whole lockeroom of sweaty fillies! Finally she lets you go, and taunts you,
"Ha! How'd ya like that one?"
You answer with a cough. Before you could be mocked again, Rarity calls out,
"Round three! This shall be the loogie round! From a distance of sixteen feet, you must hock a loogie into my awaiting mouth! Rainbow Dash, your victory has granted you the first turn."
You both move the agreed distance away, and Rainbow Dash readies herself. She clears her throat, drawing up a wad of mucus with a nasty slurping sound, then she rears back and spits. You watch in awe as the phlemmy wad flies across the field and right into Rarity's throat. The unicorn swallows happily, then opens her mouth again, waiting for your volley. You draw up some snot and spit, but your loogie falls just a little short, landing at Rarity's lap. She picks the wad up with her hoof, then slurps it down before saying,
"Round three goes to Rainbow Dash! Orange Crush must now swallow one of her loogies!"
You cringe at the thought, but you have no choice. You lay down and open your mouth. Dash stands over you, her hooves at your sides. She leans down and lets a wad of snot and spittle drip down into your mouth. You have no choice but to swallow, nearly vomiting in the process. Dash gets off of you, but not before she kicks some dirt on your side. You're really starting to get annoyed with her.
"Round four!" Rarity commands, "This shall be the belching round! Dash, as you know, you will perform first."
Rarity extends her nose and waits, as Dash primes her gullet for a belch. She swallows a little air, then opens her mouth and burps. The odor apparently pleases Rarity, and her nostrils flare. It was a good burp, but you're certain you could do better. You push Dash aside and belch, blowing a hot, rancid gust of wind that tastes like the stew you had last night. Rarity's eyes light up,
"Malodorous! Foul! Splendid!" Rarity cheers, "Round four is owned, completely owned by Orange Crush! Rainbow Dash's penalty is to experience these ravishing belches first hand, for five seconds!"
You catch Dash off-guard, and clamp her head between your hooves, before you let a smelly belch out right into her face. Dash cringes and blinks, her eyes starting to water, but she has to soldier it out until the gas has cleared. She looks a little woozy, but you bet she could keep going, so you give her another burp. Rarity interrupts your little gloating session,
"That's enough Orange, we must begin round five, the final round. It is the illustrious fart round! Crush, you shall be first."
You gulp. You're not sure if you have any farts left in you. You walk up to Rarity and present your flank. She digs her muzzle inside and you yelp in surprise, letting out a small poot. You take a deep breath and focus, trying to force all your belches down into your butt. There's a pressure in your gut, you think it's working! You push and release a long, sputtering fart onto Rarity's face. She moans in delight, the odor overwhelming her. After maybe ten seconds, the stream dies down.
Rainbow Dash is not amused. She pushes you away and lines her plothole up with Rarity's nose. She grunts, and lets out a sing loud BLART. The force blows Rarity's mane back, but only for a moment because the fart doesn't last any longer than a second! You almost feel smug, until you catch wind of the smell. Dear Celestia that is foul! It's like a hot, humid fog of stink.
As you watch Rarity sniff Rainbow's atrocious fart, you know the entire contest rests upon her nostrils. You can't bear to lose and repeat those awful tortures. Finally, Rarity announces that...