When a side character in a story performs brainless acts that gets the protagonist into trouble, or even in mortal danger, much like the monkey Abu in the movie "Aladdin". (Abu steals from everyone, the guards chase Aladdin and Jasmine down. Abu grabs a shining jewel in the Cave of Wonders, the cave collapses in on itself, etc.) In animated shows, this is often an animal sidekick, but does not have to be as such in all media.
God, Mushu has such Abu Syndrome. If he hadn't broken the stupid dragon and lift up that firework, things would be fine.