For the office drunk:
“I feel his real talent is wasted here.”
“We generally found him loaded with work to do.”
“Every hour with him was a happy hour.”

For an employee with no ambition:
“He could not care less about the number of hours he had to put in.”
“You would indeed be fortunate to get this person to work for you.”
“He consistently achieves the low standards he sets for himself.”

For an employee who is not worth further consideration as a job candidate:
“I would urge you to waste no time in making this candidate an offer of
employment.”
“All in all, I cannot say enough good things about this candidate or
recommend him too highly.”

For a stupid employee:
“There is nothing you can teach a man like him.”
“I most enthusiastically recommend this candidate with no qualifications whatsoever.”