It's not the kind of thing you ask a stranger at most parties. It's a challenge and who goes to a party to be challenged, and who does not know that? It's not

It's not the kind of thing you ask a stranger at most parties. It's a challenge and who goes to a party to be challenged, and who does not know that? It's not like the idle "So what do you do?" which can be an intentional challenge but usually is idle and innocent. It's rude and almost certainly caused by self-absorption and self-importance as they said. Any conversation could randomly wander onto a topic where the question becomes topical, so it's not that the question can never be asked legitimately at a party, but it's not normal.