First Pinkie wet herself. Then Fluttershy wet herself. While Pinkie was cheering Fluttershy up, Rarity also lost control of her bladder and had an accident in her dress, for the girls had all had quite a lot to drink before going to Carousel Boutique, and seeing Fluttershy wet herself right next to her was too much. She was embarrassed at first, a lady peeing herself like that, but Pinkie was able to help both her and Fluttershy get over it and laugh it off.
 
They didn’t notice Rainbow Dash and Applejack blushing at seeing Fluttershy and Rarity, respectively, wetting themselves. Of course if they get too excited they might be next…