1) How much money do you make?
2) How old are you? (this one can be rude....or not rude......depending upon the situation and who is asking).
3) Why are you not married?
4) Why do you not have children?
5) Were you fired...rehired?
6) Intimate aspects of relationships.
7) Did you fart? (LOL..........there might be a small chance that the farter will admit to it anyways).