When Twilight was farting, she farted a little TOO hard. She didn’t notice until Sunset pointed out the brown stain on the butt of her shorts. Naturally Twilight was embarrassed, but she just giggled nervously and got on with her day. She knew Sunset didn’t mean anything by finding it amusing, and if anything it made Sunset like her more. (She likes looking at Twilight’s butt with or without a poop stain)
 
She’ll later end up peeing herself. These embarrassing things happen to the girls all the time but they can get over it and laugh about it later.
 
I don’t do these a lot so I understand if this gets negative reception.