Of course, no one would ever wear plaid jeans.
Successfully crossbreeding plaid with jeans to get plaid jeans would cross the seams, and that would be bad. Bad in that it would cause a singularity. And that would open a portal through which the denim demons foretold in the book of Levi could invade our world and wreak havoc.
Do you really want that? To be scalded by red-hot rivet rain from on high while the world is thoroughly pantsed?
I thought not.