You don’t have to answer a question just because someone asks it. You don’t have to explain yourself to others. Your business is just that, your business. It is up to you to decide how much you want to share, when to share it, and who to share it with. If you want to answer, then do. If you don’t, it is important to be able to respond in a kind but firm manner. Many people have no ulterior motives for asking, they are just curious. You don’t need a cute or clever response, and you don’t have to be rude. A simple, “I’d rather not discuss that, but thanks for asking,” is sufficient.