The cat is at the vet because he's a spoiled asshole.

Or maybe because he has a legitimate health problem, but the vet seemed to think, after hearing my description of his behavior, that he just didn't like his current litter box. He wants the old one back. I have failed to properly raise my stupid cat.

Edit: Vet confirmed that there is nothing wrong with his guts, I just happen to have the world's most neurotic fucking cat.