[AnimalMuppet]

I can answer "describe a time when you failed" without getting sued or fired. So, no, it's not equivalently fair. Ask tough questions, sure. Feel free. This question passes beyond "tough", though, clear to "out of bounds".

[sidlls]

The questions is easily answered without getting sued or fired. Candidates are asked to describe projects they've worked on. If my question is out of bounds so is that one. After all a candidate might be sued by his employer for divulging too much about the company's internal knowledge.

One doesn't ask "name a person you reviewed negatively," of course. That would be out of bounds.