Image imported from derpibooru 
Original Description:
 
Fluttershy was feeling really kinky today so, while sitting next to Dog Spike, she peed in her dress. She is unable to hide how much she enjoys the warm wetness spreading through her underwear and forming a puddle around her as her butt gets soaked, and she is unashamed of wetting herself in front of animals, even Spike.
 
When Rainbow Dash gets there, Fluttershy will blush more than usual, but Rainbow will just dismiss it as one of Fluttershy’s many accidents. (Though she is less shy about deliberately peeing her wetsuit)
 
After doing a fart edit of this I couldn’t resist.