Refusal to compromise.
I've touched on this a couple of times, but it's worth devoting a Tenet of Humanity to it. This, perhaps more than anything else, is what Danny was about.
It's fun to observe Danny's convinctions regarding breakfast cereal.. He was rarely without his Frosted Flakes shirt. He promised his son a trip to the grocery store expressly to buy some Captain Crunch. And here we see him as he staunchly defends Total as a delicious brand of cereal. No matter how trivial it may be to you or I, or perhaps even to him, he will not let the battle go unfought.
My dad works for Colgate. I've grown up using Colgate toothpaste and have found it to be of decent quality. I have no idea why someone could grow incensed with displeasure over a common toothpaste, or how it could make one "feel like a piece of shit," but it just doesn't matter. Without meaning to, he's giving us yet another contemporary parable seasoned with "fuck" and "shit". When appreciated in a broader sense, the lesson to be gleaned is that you must hold true to what you value. Accept that others do not feel the same way, but don't let that acceptance erode how you feel. Only you can ever decide whether to modify your values.
Danny's conversation with his grandmother about Alf is one of my favorite things I've ever seen.