Rarity was looking through a chest for something, but couldn’t seem to find it. She was looking for it for so long that soon she needed to pee really badly. Rather than take a bathroom break, she peed in her shorts, taking a bit of naughty, unladylike pleasure in the warm, wet feeling, before resuming her search, eventually remembering she had left it somewhere else and finding it pretty quickly.
 
By request, a version of the last pic showing her peeing and her puddle. I don’t expect a lot of upvotes after the failure of the Twilight one, but I hope it can satisfy the requestor at least.