Question: I was writing the other day and I used the word "ubiquitous". 

While I don't think "ubiquitous" is the most egregious example of "Using Big Words To Sound Intelligent", and would be perfectly acceptable in most novels, it's just, my novel's demographic would be young teenagers, and I definitely did not know what ubiquitous meant when I was a young teenager.

Personally, when I come across an unknown word in a book, I have to take a minute to research what that word means, taking me away from the book.

On the other hand though, this could be seen as a teaching moment where I can teach young readers the meaning of new words

Answer: 
One approach to this I encountered in the novels "A Series of Unforunate Events" by Lemony Snicket (which were definitely intended mainly for a teenage audience) is to use big words as an example to **TEACH** them.

For example, the second-to-last book is called "The Penultimate Peril". In the beginning of the book, the author (who is himself a character who narrates the story) explains what the word "penultimate" means.

This was sort of a trope that would reappear in the series, but there could other ways to explain what the words means without taking someone out of the story
I would say the rule for clarity and conciseness, is if there is a word that isn’t so verbose, use it. If you are just trying to show off your ten dollar vocabulary to the peanut gallery, you are in the wrong theatre most teenagers in 11th grade have the reading comprehension of an 8th grader. I like the idea of the one person of adding it in as a gag and having the characters explain what the situation is though that would be hilarious.