The Crazy Toilet Dude is a character in the Super Mario 64 Bloopers. He loves his water closet, Mr. Toilet, feeding him Doritos and playing with him. The Crazy Toilet Dude appeared with Old Guy as well.
The Crazy Toilet Dude is one of the three minor characters to reappear in a recent Blooper after a long absence, the other ones being John Gayham and The Visitor (Gayham and The Crazy Toilet Dude didn't appear for one and a half year, while The Visitor was away for three years). However, it might just be their color codes re-used.