Interview tips - tough questions
Here is recruiter's advise regrading you closing the interview with a tough question. It very much makes sense to me, just embarrass the heck out of them so they remember you all right:

Kirch says it's profoundly disappointing in interviews to “get to the end and say, "Do you have any questions I can answer for you?" and they say, "Nope, I think you answered them all," and that's the end of it. It's just really disappointing and reflects negatively on the candidate.”

Include developing a tough question to finish things off in your preparation. “For me, I just love it when someone asks a really difficult question -- something that takes some guts to ask, asking really well-thought-out questions that show you know the business that that interviewer is in,” says Kirch. “You know their company to some extent, and you've thought about your question. It all goes back to preparation, and it tells the interviewer you thought about this interview before you walked in the door.”

The toughest opening question I encountered at the interview was:
- Have you found the place and parked all right?

I neither had driver's licenses at that time not knew how to drive. Also it was virtually impossible to park for free in the area (Boston City center).
Since we were short on cash, my S.O. was making rounds for an hour till I got our of the interview. Needless to say this was before mobile phones era.
So the question which was meant to make me feel at ease embarrassed the heck out of me since I had to start my interview with a lie.