D&D General How do you do smart chaotic evil?

[Maxperson]

Keep in mind also that those definitions are trying to portray evil in the most negative light possible, in order to make evil characters less attractive to play.

I think you're a bit too hung up on "whims" with all this, at least in the immediate sense. A whim "I'm gonna overthrow the king and put myself on the throne!" might lead to years of - perhaps on-and-off - planning and buildup in order to make that whim reality.

That's not a whim. That's dedication to a cause, which is the opposite of whimsy.