Ponies who have definitely farted in public and would do so canonically of given the chance · 7:38am Jan 17th, 2019
Just to make it clear where I stand.
Rainbow Dash - Duh.
Pinkie Pie - Canonically finds fart humor funny as of 28 Pranks Later. Childish sense of humor and a constantly-on wild side. I think it's no question she's farted out loud in front of the rest of the Mane 6 - and proudly - at least once.
Applejack - Uncouth tomboy. Literally raised in a barn. Proud of her younger sister's burp in Sisterhooves Social so farting is most definitely not taboo to her.
Trixie Lulamoon - Trixie is loud, bombastic, and rude. Thinks so highly of herself she's probably proud of even her bodily functions. Willing to bet she's crop-dusted Twilight just to see the disgusted look on her face at some point, that's so something she would do.
Starlight Glimmer - I don't have a lot to go of of for this one other than she just gives off a vibe of somepony who would nonchalantly laugh off a public fart rather than be embarrassd by it, y'know? At least current Glimmer, now that she's more comfortable being herself. Early Season 6 probably a lot less so. No matter what I think she's at least comfortable doing it near Trixie.
Moondancer - Adorkable Twilight And Friends has ingrained this idea in my head and I can't get it out. I guess all those years of isolation meant she kind of slipped on a few social norms, I dunno.
Lyra - Various miscellaneous fanworks have given me the image of Lyra as a fart-joke-loving prankster, and honestly I see it. I envision her with a sort of carefree, silly (but not, like, Pinkie-esque) personality that fart humor would fit right in to.
Anyway yeah, those are just the ones off the top of my head, there are probably a few more.
Luna would probably let them freely rip.