A: While it might be a natural inclination to tell these people to mind their own business, your desire to reply to these inappropriate queries graciously is to be applauded. While you can't say, "None of your business," you can say, "It's not the size or quality that matters to me. I just love it!" You could also say politely, "I'd rather not talk about that," or, "Why do you ask?" People often don't realize their question was offensive, and turning it back on them is a good way to prompt them to think twice.
You could also simply change the subject or use humor. If people ask, "Is that thing real?" you might reply, "It had better be or I'll have some questions for the jeweler!" If someone asks how much the ring cost, say, "Derek probably spent more than he should have, but I'll cherish it forever."—Anna Post, The Emily Post Institute