What do you say when, while trying to be lighthearted and friendly, someone asks a question that hits on a very tender personal tragedy? How do you politely let them know that, while I know you meant it kindly, that's an incredibly sore subject for me, and I'm not looking for sympathy and I don't need to talk about it, but please don't ask me that again?
Our culture doesn't do that well. I'm not sure any does. Especially when it's an issue you don't feel comfortable discussing, or an environment where you don't want to have the conversation.