Rainbow Dash lifts her leg and lets out a loud fart. She takes pride in how loud and long she can fart, and how they smell. She farts so much every day that she stinks up her shorts really bad.

(In all seriousness, it would actually be very stretchy to assume she DOESN'T fart in that outfit several times a day. We just never see it. She probably has farting contests with Pinkie too since they canonically find farts to be funny if they're anything like their pony counterparts with that whoopee cushion prank. Maybe Applejack for competition purposes, though Applejack is unamused by it.)

Just realized I never did this kind of fart edit with her in this outfit, only the bad fart cloud edit.