As someone living in Northern Canada, boots are essential!!!
I wear through most of my boots in under a year. However, I do have a pair of boots that I purchased in 1990. They are still completely waterproof and they are what I wear when the temp drops below -30°C. Without these boots, I would be in a terrible state when the going gets tough.
As someone who has been to Hawai'i more then 5 times, I have only connected the term gnarly with "awesome" or "amazing".
So ... my definition of "gnarly old boot" would be:
An awesome companion who has surpassed the test of time. Has sheltered me when times were tough and protected me when I needed it most. My "gnarly old boot" gets better with age and will most likely be in perfect shape when I am gone.
Especially if I say things like this without clarifying immediately.
Hehe, I am going to go with your explanation. That is of course what I meant.
All m even though gnarly over here usually means ugly and knobbly. Lol!!