the qestion was ...
What is the biggest screw up you have ever done at work.....that one had me for a few seconds.
I always ask that exact question. It is useful to discern how you deal with mistakes, and are you honest about it. If you learn a valuable lesson from it, it is not a bad mistake. My follow up is: "what was the biggest lesson you learn from that?"
For people in leadership position, after the "learning from mistake" related questions, I would also ask: "how much did it cost?" This one is a loaded question.
The one who answer, hmm, I don't know - this candidate is now near the door.
The one who answer, hmm... $xxx over budget - this candidate is still in, but...
The one who recognizes the cost of a mistake is beyond just the cost of the project alone, but also recognizes it has an impact to the company is the candidate with the most potential.
You may poopoo that, but think about the Samsung Note 7 battery fire fiasco. Samsung set up a whole test facility and tested hundreds of machines. That costed tons of money, but compare to the market damage and damage to the image of the company, building and running that test facility is but tiny.
Everyone in the company should keep in mind that what he/she does is important or he/she would not be there. As such, failure of that would have an impact beyond the immediate project and project staff, however big or small.
That recognition is important. Any inkling of that recognition shows this guy is
not just a pigeon looking for a hole.
A related question is "What was the biggest crisis you had to resolve?" The
follow up question is a trap: "Oh, wow, that was an interesting one! How often does it happen?" (or similar)
Crisis will happen, you can't prevent them all. So, there is no issue with that.
But, a crisis should not repeat. The candidate should have learned from the first time this crisis occurred, and put in measures to prevent it from repeating. If the same big crisis happened twice, you are missing something. By the third time, you are not doing your job right. If the candidate replies: "Oh, it happens every now and again..." Unless an explanation followed the comment unsolicited, this guy is an idiot. He/she never learns, or is simply didn't matter to him/her. If the unsolicited explanation that followed was "it is a pain, but the cost of fixing it is too high", that would have been acceptable.