This comment on the recent thread on misspelled phrases reminds me of one of my pet peeves:
I find "mentee" so offensive that I disparage its usage at every opportunity. While I will reluctantly overlook the use of "Mentor" as a verb (that battle is lost), I refuse to acknowledge the existence of the verb "to ment" that "mentee" necessarily implies. Resumes containing this word require no further review. I recently returned a fundraising letter in its business reply envelope with the word circled and the written comment, "This is not a word." I reserve such vitriol and summary dismissal for this error alone. This is because it is what might be called a Homeric error. And I don't mean Homer Simpson. Please warn your students against this fatally discrediting usage.
Here's one thing I find so offensive that I disparage its usage at every opportunity: The use of a phrase "is not a word" -- which you'd think would have the standard meaning of, well, "is not a word" -- to mean "should not be a word" or "is a word that annoys me." English speakers use "mentee," and use it often enough that it's gotten into the OED (attested for over 40 years), as well as the Random House Dictionary and the American Heritage Dictionary. It is, which is to say "is," a word, which is to say "a unit of language, consisting of one or more spoken sounds or their written representation, that functions as a principal carrier of meaning" -- with the function and the meaning attested by the authorities in the field (dictionaries).
I have nothing against complaints that some word or phrase is inelegant or confusing, or admonitions to students that using some word or phrase will lead some readers to think the less of them. The earlier thread was all about collecting data for such admonitions.
But those complaints should, I think, be put that way. They should not be made by claiming that something is not a word when it is a word under any sensible and common definition of the term "word."
(Note that there may be an exception when the claim is clearly hyperbole, but here this exception doesn't apply: A reader may well assume that "mentee" is actually an uncommon error, rather than a usage that is common enough that it has been recognized by lexicographers as a normal part of the English language.)