Not so much of an insult as it would be if they tell you to "put a mask on".
Especially if it was Halloween and they only just asked you to take it off, because it was scaring the children.
Sounds like a snarky, shallow girl. Ignore her. She is trying to dis you. If she doesn't get a rise from you, she will move on. Take care, and Good Luck!!
It means, why is your shirt always off? Put it back on.