what else could I say??

[Archangel]

Honestly, I don't understand why people get offended when asked this question. Now, I know every situation is different, but I would first assume that if I was asked "What do you wear under that?", the person asking the question isn't asking what I, personally, am wearing under my kilt, but is actually meaning "What does one wear under the kilt as opposed to pants?" And honestly, is that not a valid question?

Oh, I know most people probably ask because they've "heard" what's not worn under the kilt, but they probably just want to know the truth of the matter. Perhaps they think that's there's a special garment to wear under the kilt, or what is more widely worn, possibly due to comfort or what not.

I would try to explain that traditionally, nothing was worn underneath, but really it's to person and what they find most comfortable. If I was asked directly as to what I was wearing. Depending on the situation I was would probably say something like "Sock and shoes", "I prefer to go regimental," "That's a bit personal, isn't it?" with a smile. Honestly, I don't any reason to rude unles the person is being rude to your first.

I guess I have a bit of a disagreement here. From your first paragraph, I start from the premise that asking anyone about their underwear, or lack of, is not a valid question.

I remember as a child my mother showing me the mail order catalogue (way back, way, way back), and turning to the size chart page where there were drawings of people in their basic underwear. She said that nobody but a doctor was allowed to touch, look or ask about the area that covered. In all my years I have come across no reason to disagree with that teaching (well, until my late teens anyway).

Generally, I am polite, because I'm a nice guy, but I start from the premise that it is a rude question. They don't have a right to know, they don't have a right to ask. So, depending on the context, they could get any range of answer and on this my conscience is clear.