If I remember the commentary correctly, they were originally going to make Mr. Spatula turn into Mack Salmon in Moai Better Blues, but Steve didn't want Mack Salmon to have any sort of backstory.
"Always expect the best of others... And watch as your hope is crushed like crackers in a fat man's bed. And the fat man is angry. And the fat man has a sledgehammer. And the fat man is yelling 'DIE, CRACKERS, DIE!!'"
- Rat, Pearls Before Swine