Baboonism
When your butt is so sore from not wiping properly that you start scratching it like a monkey in a zoo with a cheeseburger.
I sat on a rusty chair and now my butt is scratching like a baboon on a banana.
She had to scratch her butt in the middle of class. Baboonism.
He was so itchy, he scratched his butt in front of his boss. Classic.