Most people understand "narcissism" to be pathological behavior. If you use it to not mean pathological behavior, most people are likely to not understand you.
I’d be careful with “most people” claims. A narcissist is in the dictionary as “a person who has an excessive interest in or admiration of themselves.” That includes above average, not limited to a pathology (which people who are not doctors are unable to diagnose). I’m certain I’ve heard and/or said something along the lines of ‘oh he’s a bit narcissistic’ multiple times in my life. Having completed an advanced degree, I’ve met quite a few researchers I think are reasonably described as being a little narcissistic about their work.
I object to projecting your own personal non-dictionary definitions on others. Are you thinking of clinical Narcissistic Personality Disorder? That is not the same thing as Narcissism.
My personal usage and understanding is quite close to the dictionary definition (https://www.dictionary.com/browse/narcissism): inordinate fascination with oneself; excessive self-love; vanity. Those are not positive traits, which goes back to my original point: if you use the term not intending to imply something negative about the person, you're likely to confuse others. That confusion is why this subthread exists.
@mjburgess was using it to refer to negative attributes, and so was I. You stretched the idea into something it's not by saying it has to be "pathological", and that it has to negatively impact others, and you claimed that unless people adhered to those criteria, the term wouldn't be understood. Neither of those claims of yours is supported by the definition you just provided, nor have you demonstrated that "most people" agree. Narcissism can be a negative attribute about someone without being pathological and without affecting other people in a material way. Being narcissistic is judged as a negative attribute to have by the dictionary.com definition with the purely subjective words "inordinate" and "excessive", but it doesn't otherwise agree with what you said above.
I am unaware of any colloquial use of "narcissism" that would include going to grad school to learn more about a subject. Poster steev was also confused by this usage. You are correct, I have provided no evidence our confusion will be universal, but: don't be surprised if it is.