The Guy At Work (GAW) at my new job is one of those guys who likes to tell women to "Smile!" The first time it happened, I let it slide. The second time it happened, I stuck my tongue out at him. But today, the third strike, there was only one other person working, and she was on the phone. So I finally stood up for myself.
GAW: Smile, Sarah!
Me (not smiling): Please stop telling me to smile.
GAW (looking like someone just slapped him): Oh, you're having a bad day?
Me: No, my face always looks like that.
GAW: Like you're having a bad day?
Me: Yes. It's unfortunate, but that's just how my face looks.
He hasn't said much to me since then. I think I got my point across though.
Just to clarify, I'm not a grumpy person or whatever. I'm just sick of people (most often men) telling me to smile. I don't care if you think I look angry or pissy or ugly. That's my face, and it always looks like that. I'm not obligated to change it just because you don't like it.