"What would you do on a typical day to stay busy during down time?" This threw me a bit because I had never worked at a bank. Another difficult quesiton was, "Tell us about a time when you offered a suggestion to an employer to make a process more efficient and it was applied?"
I was prepared so well for the interviews that I didn't feel that there was a difficult or unexpected question, otherwise I would say "how many years of customer service do you have". The typical "what are your strengths?" that is typical for any interview is always somewhat difficult for me but not too bad. A question about my most difficult customer encounter highlighted my ability to de-escalate difficult customers.