Apparently, not only can cats use a toilet... They can teach themselves to do it.

When Sarah Way woke up in the middle of the night, she found her beloved cat, perched atop the porcelain throne, going to town, doing its business. Props.

On the other hand, I would hate to have been the cat... Perched atop the porcelain throne, going to town, doing my business, and have my master come in and pet me at my most vulnerable. To each their own I suppose.