Fastidious J. Spiffington is a recurring villain from the Jetix series Yin Yang Yo! He is a small hamster with a cultured British accent, obsessed with cleanliness and world domination. Fastidious is nearly always seen inside a hamster ball that serves as the control center for his robots, mainly his Hamsterbot. He has a habit of drastically increasing his pitch whenever exclaiming certain words, such as "Activate!!" He seems to be a certified attorney. Fastidious made his debut appearance in the episode "Neat Freak", when he ran into Yin at the cleaning store. He managed to goad Yin into capturing a trio of elemental spirits, and nearly succeeded. However, Yang was able to find out Fastidious was the real evildoer, and with the spirits' help, the rabbit twins beat Fastidious.
- There is a Running Gag about Fastidious claiming himself as a hamster despite anyone saying that Fastidious being a gerbil.
Fastidious is a Hamster With Yellow Fur, Black Whiskers, Light Cyan Rings Around her left Eye, One Purple Eye just Like Yang and One Cyan Eye, Pink Nose, and Wears a PJ Suit with a White collar and a red bow.