This reminds me of something that happened to me a couple months ago...
I was walking into a store near where I live and I passed this girl. She stopped me and said, "Hey, you dropped something." She pointed to the ground behind me and I turned to look. She kept saying "See it's right there." I couldn't for the life of me find what she was talking about. Then she says, "Right there, your smile!"
I gave a laugh and walked away as fast as I could without looking strange. I beat the hell out of myself the whole rest of the day and some days afterward.
Having it blatantly pointed out to me by a stranger, especially a female, was so not what I needed at that moment.
At some point in high school I started putting on a blank face that kind of makes me look really, uh unpleasant. I did it to discourage people from talking to me. I can't turn it off. It's now the natural way my face forms. I've gotten comments about it. Kind of like the example above. Girls would say I looked scary. Sometimes I try to undo it when I'm in public so I don't look scary, but it feels awkward and I don't know what face muscle to use and I get worried that I look strange because I am maybe making a facial expression that looks unnatural.