Sounds like you ran into a little brat that was determined to demonstrate her poor upbringing. Don't take it personal. There is no shortage of people with low self-esteem that feel compelled to share their misery.

Walk proud and tell the next brat that when your choice of personal attire becomes any of her business, you'll be sure to let her know. Maybe remind her that in at least 12 countires, she would be STONED TO DEATH for what she was wearing and you would be willing to fight to save her life, in spite of her obvious ignorance, if she would dane to allow you to do it kilted.