You decide on hitting up a very ladylike pony, you're certain she'd be extra-disgusted by your gassy emissions. Watching her for a bit, you notice she's carrying a couple saddlebags full of fabric, and must be a seamstress of some sort. That allows you to form a nice plan, one to get her in a very awkward position without raising any suspicion.
You grab a small shawl from your own saddlebag, and wrap it around your waist, forming a little skirt. You rip a little bit of the skirt at its end, creating a small, but noticeable tear.
"Oh excuse me! Excuse me miss" you manage to catch up to her, and present your torn skirt to her, " I've heard you're an excellent seamstress, could you possibly take a look at this rip?"
"Of course darling," she says, and walks around your backside.
"I know it doesn't look like much, but please examine it carefully." you say, trying to lure her into getting closer to your rear.
She obliges, unwittingly bringing her snout closer to your butt. You wiggle your flank a little closer to her, and she leans just a bit closer, squinting to get a good look. You decide this would be your best chance, and you push backwards with your butt, slapping her with your cheeks. Then you let the best blast of flatulence so far fly right into her face!
The fetid gust literally blows the poor mare's hair back, and instantly floods her senses. It's like a typhoon in a sewer, and poor Rarity's right in the middle of it. She goes green with nausea from the awful stink, and tries to pull away, but you slam your butt into her snout wedging it in between your cheeks. From there she has no escape from the gaseous stench, and has to endure the fart for ten more seconds before it dies down.
When you cease farting, Rarity tries to struggle away, but your cheeks clench her still.
"Stop this this instant you stinking animal!" she sobs, she can't take much more of this.
"No way sweetie," you say back, "I've still got plenty more gas. Open wide, this one's gonna be juicy!"
Your belly gurgles and...