Ethics Option 2: A Question of SanityEdit
Some DMs will want Law and Chaos to mean essentially "Sane" and "Insane". That's fine, but it doesn't mean that Chaos is funny. In fact, insanity is generally about the least funny thing you could possibly imagine. An insane person reacts inappropriately to their surroundings. That doesn't mean that they perform unexpected actions, that's just surrealist. And Paladins are totally permitted to enjoy non-sequitur based humor and art. See, insanity is when you perform the same action over and over again and expect different results.

In this model we get a coherent explanation for why, when all the forces of Evil are composed of a multitude of strange nightmarish creatures, and the forces of Good have everything from a glowing patch of light to a winged snake tailed woman, every single soldier in the army of Chaos is a giant frog. This is because in this model Limbo is a place that is totally insane. It's a place where the answer to every question really is "Giant Frog". Creatures of Chaos then proceed to go to non Chaotically-aligned planes and are disappointed and confused when doors have to be pushed and pulled to open and entrance cannot be achieved by "Giant Frog".

If Chaos is madness, it's not "spontaneous", it's "non-functional". Actual adaptability is sane. Adapting responses to stimuli is what people are supposed to do. For reactions to be sufficiently inappropriate to qualify as insanity, one has to go pretty far into one's own preconceptions. Actual mental illness is very sad and traumatic just to watch as an outside observer. Actually living that way is even worse. It is strongly suggested therefore, that you don't go this route at all. It's not that you can't make D&D work with sanity and insanity as the core difference between Law and Chaos, it's that in doing so you're essentially making the Law vs. Chaos choice into the choice between good and bad. That and there is a certain segment of the roleplaying community that cannot differentiate absurdist humor from insanity and will insist on doing annoying things in the name of humor. And we hate those people.