I just saw one, called "Backpack Attack", where
Spoiler Below Jackie Khones asks Bloo about Mac's backpack, which makes Bloo want to know "What is UP with his backpack??" One of Bloo's ideas involve spitting orange juice on Mac's red t-shirt. When Mac takes the shirt off...
The white sleeves turn out to be a WHITE SWEATER.
But Bloo still doesn't give up, and tears his backpack off, and dumps out the contents, revealing basic school junk.
THEN Jackie asks Eduardo "What's up with Coco's eggs?" which leads Eduardo running after Coco, and then the short ends.