Unbetterable 

Not able to be improved

That article is unbetterable

Unbetterable by Tiggerr August 10, 2012

unbutterable 

A person who is not susceptible to another persons attempts to be buttered up

Trying to butter me up innit……unfortunately I’m unbutterable

unbutterable by Specky1984 February 21, 2014

Unjesterable

unable to be rage-baited in any form or function,

"I tried to wind my brother up about his favorite football team losing, but he just laughed it off. He's completely unjesterable; nothing I say gets a reaction out of him."

Unjesterable by Aristotle The 2nd January 10, 2026