JimB, great answer. You don't need any advice from me, but here are mine.

Short answer: A light summer-weight mystique.
Short answer: What kind of underwear are you wearing?

More detailed answer, for use when asked by an attractive lady:

Well, it depends. If I'm running 5 kilometers at the highland games, one option might be appropriate; for everyday wear, another option. When I'm asked that question by an especially attractive lady, a third option comes immediately to mind.

The object, of course, is to see if we can make her blush. If not, try the "If you were a lady..." line.