The act of ruining or soiling
something that it is preferred would be kept in nice condition. Traditionally applies to brand
new merchandise,
cars, glossy or glass screened electronics, and other consumables.
"I opened the
box for my brand new $300 universal remote to find that some
asshole had already gunked it up with his skunk fingers and probably returned it."
"Oh shit, is that the new iPhone X*?? Can I see it???"
"No, you'll gunk it up with your skunk fingers!"
*
Whatever the latest COOOLEST one is.