I had to dig this up today, and thought it might be useful to others as well. Any additions? From the Lexicon of Inconspicuously Ambiguous Recommendations (LIAR):
You’re called upon for an opinion of a friend who is extremely lazy. You don’t want to lie — but you also don’t want to risk losing even a lazy friend. Try this line: “In my opinion,” you say as sincerely as you can manage, “you will be very fortunate to get this person to work for you.”
To describe a person who is totally inept: I most enthusiastically recommend this candidate with no qualifications whatsoever.
To describe an ex-employee who had problems getting along with fellow workers: I am pleased to say that this candidate is a former colleague of mine.
To describe a candidate who is so unproductive that the job would be better left unfilled: I can assure you that no person would be better for the job.
To describe a job applicant who is not worth further consideration: I would urge you to waste no time in making this candidate an offer of employment.
To describe a person with lackluster credentials: All in all, I cannot say enough good things about this candidate or recommend him too highly.