First rule of business, customers create revenue - no customers, no revenue. Revenue pays salaries. It's never good business practice to be rude to customers.
You never know whether you're talking to a customer who flies once a year or the CEO of a major corporation who has 100's of employees flying multiple time per week. If you treat every customer as if they were a CEO, it will always be good for business. This is just business 101.
No matter how bad the question. A simple smile and a quick explaination always works best.