I thought I remembered hearing years ago that it would ruin the whole system. Could be wrong.
a pin hole in a rubber brake hose would cause the slow and likely unnoticeable loss of brake fluid. at some point. the system would fail.
You got it right. Coax cable depends on high resistance/impedance between two conductive shells to permit waves of many (high) frequency to propagate at the same time. The pin cuts the resistance to nearly nothing...
It won’t ruin it but it will go on the fritz and trouble shooting the problem is a real B!#$@. Would drive a technician nuts for hours untill he decided to change out the whole cable.