This is a word that everyone should know. I don't know why Webster 1913 didn't autonode it, because it reportedly is an American English invention, first seen in the early 1800s and still used today. It's thought to have evolved from discompose or disconcert, perhaps being merged with bobbery. Since the word was a modification of an existing dis- word, it follows that there is no word combobulate.
to confuse, upset, or disconcert.
That's about all there is to it. Simple to use, erudite yet pleasing to the ear. Noteable fictional characters who spout "discombobulate" include The Pest (Alvin Fernald's little sister), Blackadder, and Abe Simpson.
Let's consider one example of the correct usage of "discombobulate":
Dr. Nick: Hi everybody. Now, tell Dr. Nick where is the trouble.
Abe: I'm itchy! I've got ants in my pants! I'm discombobulated! Give me a calmative!
Dr. Nick: Slow down sir! You're going to give yourself skin failure!