Issue with making everything plural, including a person having butts

I have noticed this oddity with my manager for a while. He tends to pluralize words that do not require an s at the end. As an example, he will say documentations instead of documentation.

We had this conversation the other day:

"I had to work my butts off to finish this work," he explained.
"Butts? You have two butts?" I asked curiously.
"A left and a right," he said, bursting out laughing.
"No, you have two butt cheeks. You have one butt," I explained.

Who knew that I would be having a grammatical discussion about butts and butt cheeks in my workplace as a professional. Fun!