Party Central (theatrical; 5:41)
Disney Movies; IMDb; Pixar; Pixar Wiki; Wikipedia
streaming sites: Disney+

This played in theaters before Muppets Most Wanted, but it's actually based on Monsters University. I first watched it online, on Disney Movies Anywhere (though it has since been removed from the site). It's available on the Pixar Short Films Collection volume 3. It's a seriously funny story of Mike and Sulley helping their fraternity brothers steal an awesome party from a more popular frat. Plus there's a good post-credits scene.