General:
* Pig-headed
* Obstinate
* Headstrong
* Willful
* Inflexible
* Cantankerous
* Bullheaded
* Mule-headed
* Thick-headed
* Closed-minded
More Harsh:
* Hard-headed
* Dogged
* Unyielding
* Intransigent
* Recalcitrant
* Perverse
* Unreasonable
* Obtuse
* Insensate
Humorous:
* Set in their ways
* Stuck in their ways
* A brick wall
* A mule
* A stubborn as a mule
The appropriate dysphemism will depend on the context and the desired level of negativity.
Remember, dysphemisms are often used to express disapproval or to be insulting. Use them with caution!