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: 
You can always put doubtful words in a **glossary** - a mini dictionary at the end of your book with definitions.
Klippy, your intuition is correct.

Your audience comes first. It’s the reason why you write the book. It doesn’t matter who else reads it, its only important that it pleases your audience. A pleased audience then tells others about your book via word of mouth (i.e. those outside of your audience). Your audience grows and you earn authorship recognition.

It may be a great learning opportunity to learn a new 25 cent word, but that such writing belongs to a textbook author whose target audience are students, not a fiction writer whose audience seeks a moment of time where the your reader escapes reality in your story world.