I am a 'show me' kinda guy. I'd like to see a case where a HO policy did not cover the costs when a borrowed lawnmower that is being used by a neighbor threw a rock at a neighbor's Ferrari and put a $20,000 chip in the paint or took somebody's eye out. (hypothetical examples of course)
You say there is zero negligence in the OP's case so an HO policy will not pay. I highly doubt it and would like to be shown otherwise. Got any actual examples to back your position?