I needed to go to the Post Office the other night but I wasn't sure when it closed, was it 7 or 9? So I called and confirmed that it closed at 9.
While I was there purchasing stamps and mailing notebooks, the phone rang and the postal worker sighed quite loudly. "Busy night?", I said. "Yea", she said, "Probably another dumb question like what time are we open to". She then proceeded to answer the phone not knowing that I was the one that had posed that 'dumb' question earlier in the evening.
So here's my tip....when speaking to a customer be careful what you say is dumb, you never know who you are talking to!