No matter what they want to tell you or wich question they need to ask, don't respond for at least 15 seconds. Keep looking at them with a friendly expression on your face, your body language being open and inviting. It'll give them time to realise how stupid their question really was and how insolent they where to claim your valuable time. If, after 15 seconds of unbearable silence, they didn't withdrew with their tail between their legs (wich they usually will do) you just bought yourself 15 seconds extra to make up a another of your brilliant answers.

(Wilco van de Most)