Fluttershy is a slob.

There is a fact little known amongst Ponyville; amongst Equestria in fact. This is a fact which may, admittedly, compromise the pretence of one particular pony, but I feel that the world should know of it.

Fluttershy is a slob.

Surprised? You should be. When thinking of Fluttershy you will generally think only of one sweet, demure little mare who cares for her animals, and more importantly her friends.
You haven't seen her when she thinks nopony's looking.

She spends a lot of her day just sitting down on her flanks, reading through the same book over and over because she can't be bothered to change it.
When she eats, she eats large; she gets herself the largest portions from the greasiest, most artery-clogging establishments in town.
She proceeds to sit and eat this food straight out of the bag it's been given to her in or occasionally just off of her belly.
When she eats, she doesn't eat with delicate sweetness and slightness, she wolfs down abnormally large mouthfuls of junk and beats her chest when the food goes down slowly.
After every few bites of food and especially every sip of her drink, Fluttershy purposefully releases a loud, roaring belch which seems to suit a fully-grown stallion more than a mare.
When the food begins to go to her thighs, and it does, she doesn't care.
She takes this acquired chubbiness as a blessing, as it means that her farts come out more juicy.
On the topic of farting -- and it's a major topic for her -- I'm afraid I can't tell you the entirety of it, as at points the smell has grown so terrible nopony could be near to know.

When Fluttershy decides to let rip, she does so with a forceful feminine grunt, and flicks a grin of satisfaction when she hears the deepness and crepitation roll out like thunder from beneath her.
She just sits back and lets herself bathe in the souring, foul gases which slowly begin to rise and swim around her.
She sniffs contently at the garbage-scented miasma, and does no more than perhaps release another growling burp to just add to the smell and see how bad she can get it to be.
She sometimes likes to have farting contests with herself, using her animal friends as non-consenting judges as she tries with each bubbling, groaning emission to better the last one.

When they start to struggle in her thighs and scratch to escape their prison, Fluttershy does nothing. She just watches as the life slowly is sucked from them before her eyes and the noxious pollution her ass is billowing and letting slip wetly finally becomes the last breath they ever take.
Sometimes, the farts inject into her furry friends so deeply down their gullet that it rises back up into a post-death belch, which Fluttershy merely laughs at.

As far as stink goes, Fluttershy is perhaps one of the stinkiest, and doesn't even know how long it's been since her last wash. Her armpits, the most humid and sultry confinements you'll find in all of Equestria, possess B.O so obnoxious that you'd be able to smell its sharp bitterness from across the room.
She lifts up her arms and grins at the bush of hair underneath -- beaded with sweat and stink. If she's feeling especially naughty she'll like to belch right into her armpit and force an unluckily by-standing animal to sniff it close up; holding them there until they can't hold their breath anymore and their body forces them to take in a deep breath and pass out. When said animal finally becomes conscious again, she just does the same until they pass out a second time.

If her armpits can make animals pass out, then you would guess that the pit between her thigh and loins is a million times worse.
Her whole lower body is explicitly unclean, and radiates an odourous, almost cheesy aroma.
She hasn't cleaned her pussy in the longest time, and as a result of this has left it stinking like rotting fish. The buildup of smegma and crust has grown so overwhelming around her lower body that even when she's farted, Fluttershy can still smell the deathly scent.

The elephant in the room, and the thing which I regret even mentioning, is Fluttershy's toilet habits.
When she feels like she needs to shit out whatever manufactured combination of junk food she's ingested, she decides what to do next based on how big the shit feels.
If she has to take a huge dump, she'll trudge to her bathroom and slap her fat ass down onto the seat, moaning softly to herself as her anus winks a wet, popping trail of gas before it gapes and begins to spew out her sloppy, copious shit.
It releases in thick, reeking packages of pony dung which splash her ass in toilet water until the shit out-ratios the water in the bowl.
When she's left her steaming mound in the toilet, she just leaves it in this state.
She would flush, but she just knows that she'll block the pipes.
Fluttershy uses her toilet in this way until her residue rises to the brim, when she flushes it several times until it doesn't fill quite so high.

If she doesn't judge that he has a lot of waste to pass, she'll just do it on her couch. This seems perhaps the most animalistic and disgusting thing a female can do, but Fluttershy simply doesn't care.
She'll rest back and start browsing over book again until she feels her thighs warm and wetten with a little rivulet of her piss. It stinks like fish, and stains her couch in a dark patch.
When the trickling piss dies down, she begins to deposit her solid waste, and sighs as she feels the greasy, gritty matter grow from under her. She shifts herself with a grunt to allow the excretion better passage: worming out and slopping over onto the floor with a wet splat.

She just lets the shit dry up around her butt to add to the cumulation of crusty feces that's already there.
On occasion, Fluttershy will misjudge her gaseous expulsions, and end up caking herself in a little more than just the stink. When, on said occasions, when the noise of Flutters' ass grows from a husky rasp to a juicy, squashy sputter the only thing she'll do is sit back down in her waste and feel satisfaction as it coats her lower thighs.
The perpetual stink of her cottage is ungodly up-close; she manages somehow to perfume it up enough to mask it when her friends visit.

Fluttershy is not aware that anyone knows her secret lifestyle, apart from her animals -- but of course they'll never tell.