Costume vs. Outfit/dress

While we are on the subject of "costumes", it drives me up the wall, when people ask me if I am wearing a costume when I am in a sari/salwar kameez. I know technically costume also describes an outfit that is from a particular country, etc. But I don't see people saying, "oh you are wearing an American costume," when you are in jeans and a t-shirt! It's a national dress or just a dress/outfit.

Also, wearing an outfit implies that you are representing that particular nation, etc. Well, it feels kind of strange. I am Indian and hence I am not really pretending to be Indian wearing a sari. That's my cultural dress. Neither am I in costume when I wear Malaysian dress.

Oh  it's a little thing. I know, no bad intent is behind the use of the word. Just it throws me off every time! ;)