I read this story (in fact, a novella) at least 40 years ago. Probably in a collection.
A team of scientists is sent to investigate the value of a newly discovered planet. With them there is also a rather special young man, just a kid, with his mentor. The kid is a living encyclopaedia, with an eidetic memory. But he has a clear problem with social interaction. A kind of "Rain Man". In technical parlance, he has the Asperger syndrome.
I forgot most of the story, except for a specific incident.
At some point, the kid called one of the scientists a "non compos", and the latter got extremely angry, understanding this as "nincompoop". Fortunately, the kid's mentor was able to calm the situation, explaining that in the special school the kid went to, where all the other students were similar to him, they called all the other people by the latin formal phrase "non compos mentis", "not of a sound mind", shortened to "non compos". What the kid said was thus a formal Latin phrase and not the rather colloquial term "nincompoop", and therefore was more acceptable.
In fact what the mentor essentially meant was that saying, in Latin, "I seriously consider that your intelligence is quite subnormal" is not as bad as saying "Triple idiot!!" but the scientist did renounce to seriously beat up the kid.
What is even more funny is that though the origin of the term "nincompoop" is not quite clear, there are several hypotheses, one of them is that is does come from "non compos (mentis)". But it is colloquial, much worse than a synonymous formal Latin phrase....
I don't think this incident was really essential. But is it enough to identify my story ?
EDIT
Kudos for Andrew for answering my question. Since it is a duplicate I got some info from the other pages.
This helps, because Andrew did provide a link, but without search engine to check the accuracy of my memory. which is not too reliable.
For instance I found a quote
Additionally, the individual irritated the captain of the Triple-G space ship.
And as he was about to leave, the captain called out, "Sheffield!"
"Yes?"
"What in Space is a 'noncompos'?"
Sheffield suppressed a smile. "Did he call you that?"
Sheffield is the one whom I called "the Mentor". So it was not a scientist that the kid called "noncompos" to his face but the spaceship's captain. Who clearly was able to restrain himself since Sheffield was not present at the scene.
Now I have a doubt. The kid used "noncompos", certainly, but did the captain actually utter the word "nincompoop" in a sentence like "How do you dare calling me a nincompoop?" or did I "hear it" in my mind when reading the incident ?
If the latter is correct, I wonder how on Earth I knew of this word at the time, considering I am French. Of course, I probably read this story while I was a student in the US in the late 70's.
NEW EDIT
Well, I found the right place. The captain never utters the word "nincompoop", I invented it, from his reaction which strongly suggests that this is how he understood Mark's "noncompos"
“You’ve got no say in it, you . . . you noncompos.”
The captain’s coolness evaporated. He threw his cigar down violently and stamped at it, then picked it up and poked it carefully into the ash vent.
“What the Galactic Drift is this?” he demanded. “Who are you, anyway? ...
Only the cigar, not Mark, suffered from the captain's losing his coolness. And he did not refer specifically to the phrase Mark had used. But my mind interpreted it as "he understood nincompoop".
