Quick answer
Given a choice between a grieving bear and a committed fool, take the bear. The verse means it as more than a joke.
Read both lines
The comparison is shocking on purpose, and the reason it works is that a bear robbed of her cubs is at least predictable: she is enraged for a reason, and the reason will pass. A fool in the middle of his folly has no such logic, cannot be reasoned with, and will not stop when the cause is removed. That is the argument. What makes someone dangerous in this book is rarely strength; it is the absence of anything you can appeal to, which is why the previous verse's hundred blows changed nothing.
Related: Proverbs 17:10 · Proverbs 27:3 · Proverbs 26:11
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.