[sigg3]

It might hurt the feelings of HR at the new place where he wants to apply though.

No one disagrees with you in principle, but there are realcitrant social practices punishing this kind of feedback. It is always taken as a grudge rather than an observation, and this makes you less attractive as a hire.

[Dalewyn]

This goes the other way too: Generally speaking, companies are expected to refrain from negative commentary when contacted as a reference by subsequent employers. The only exception, and seldom done, is if the employee was terminated due to egregiously bad circumstances.

That is to say, (former) employee doesn't speak ill of (former) employer and (former) employer doesn't speak ill of (former) employee. It's how society keeps itself oiled.