Artist’s description:  
Scootaloo is feeling mischievous, and Sweetie Belle is the unlucky filly on the receiving end
 
Story in the comments:  
It wasn’t that Scootaloo didn’t LIKE Sweetie Belle, but her ideas were… well, boring. Scootaloo would say jet skiing, Sweetie would say paddle-boating. Scootaloo would say winter sports, Sweetie would say building snowmares. Scootaloo would say alligator wrestling, Sweetie would say… Well, you get the idea. The most exciting idea Sweeetie had ever proposed was “Scooter tricks” but what kind of idea was that?
 
Worse, Apple Bloom was with the rest of her family, working to pick a huge bumper crop that had come in, so she couldn’t balance the two out. So, they were left to their own devices.
 
Sweetie was pacing back and forth in the clubhouse, racking her brain for ideas. She was still wearing her school uniform - a long sleeved blue shirt and a blue jumper with a red skirt. Scootaloo always hated those uniforms, and a wicked idea started to form.
 
“Hey Sweetie, I know what we can work on. Reflexes!” The little unicorn stared, puzzled. “Reflexes?” “Yeah! We’ve gotta think fast and act fast! Now stand over there and turn around” Sweetie obliged, hesitantly. She feared Scootaloo’s ideas as much as Scootaloo hated hers. Still, this didn’t seem so bad. Nothing was on fire, there weren’t any sharks, and why did it get so cold all of a sudden?
 
Sweetie looked down in growing horror, her ears flopping down. Scootaloo had just ripped her skirt off, revealing her flowery, frilly undies! Scootaloo smirked “Really, Belle?” “H-hey, they’re pretty. And that was sown on! Rarity’s going to kill me…” “Well, that’s why you’ve got to work on those reflexes! You never know what might-” And with a yank, her own shorts were on the ground.
 
This meant war.