I'm currently reading David Resnik's The Ethics of Science (not a bad read at all, by the way) and in Chapter 7: Ethical Issues in the Laboratory I encountered this heading: The Ethics of the Mentor-Mentee Relationship.
That brought me up short. Mentee? No such word. In fact, my inbuilt spelling corrector presented it first as manatee :)
Ending in -or makes mentor look to the unwary like the agent noun of a verb to ment, which would permit mentee as the passive noun. Alas, mentor is a noun, sure enough, but it's actually a proper noun, the name of Odysseus' pal whom he appointed as guardian and teacher of his son Telemachus — as every skoolboy kno. His mentor, in fact.
This is what happens when people form words without proper philological and literary education. Mentee is first reported in the American Economic Review from 1965: What is the typical economics class but a contact between the conservative teacher and his mentees? We owe to Lord Chesterfield (he of Letters to his Son fame, in 1750) the first recorded use of mentor, with the (hyper)correct capital M and italics: The friendly care and assistance of your Mentor.
Mentoree would, of course, be the correct form of the passive noun of the verb to mentor, if we don't mind nouns being arbitrarily verbable; but the agent noun would end up as mentoror. Ugh.
If I ever catch any of you using attendee to mean "someone who attends a conference or meeting" I shall growl. It's far too common and egregious a mistake. Remember: -er or -or end agent nouns; -ee ends passive nouns. An attendee is someone or something which is attended, not which attends.
And, still on the subject of things that have things done to them, yesterday I found the phrase "Rats used as guinea pigs in medical experiments". Someone obviously suffers from metaphor blindness.